Know which questions are eating your marks.
Free speed training on 70 JEE questions across 25 topics — Chemistry, Physics, Math. JEE Main grading (+4 / −1). No account needed to train.
Stop Memorizing Tables: Crack JEE Spectroscopy in 20 Seconds
Find a topic or question
25 topics · 70 questions · hack sheets & concept labs. No sign-in needed.
Speed is a subject.
JEE isn't only about knowing — it's about time economics. This trainer measures what every solve costs: Time-Efficiency Ratio (TER), Topper-Velocity zones, time leaks, and guess-vs-concept diagnostics.
Pick your exam — tap a card and your run starts immediately.
Run complete — waiting for connection
Your answers are saved on this device; results will appear when you're back online.
Your velocity map
Greed = wrong answer with a first tap faster than the question's guess threshold (a guess-flag, not a judgement). Concept-gap = wrong with a genuine attempt.
Your exam-economics card
Share it with your study group — this is what a test series never tells you.
Results for “”
How the trainer works
Pick a set, beat the clock, and learn what every solve costs you. Everything below describes features that are live right now.
Speed runs
Speed-Run (JEE Main): single-correct questions, big timer, streaks. Marking +4 / −1 — beat the hack pace shown on each question.
Tactical Mode (JEE Advanced): multi-correct checkboxes with a risk panel before you submit. Marking +4 if everything you ticked is right, +1 per correct option for a partial attempt, −2 if anything you ticked is wrong. Untick what you are unsure of. No account needed — training is fully anonymous.
The trainer's bank is a growing set of 70+ JEE-style problems across topics (and counting). A full JEE Main paper presents 90 questions of which 75 are attempted — topic sets are training units, not full papers.
The four zones
TER (Time-Efficiency Ratio) = target time ÷ your time. After a run, every attempt lands in one zone:
- Topper — correct and fast. Topper velocity. Hold the pace.
- Time-Trap — correct but slow. Hesitation is the leak, not the concept.
- Lucky Guess — fast and wrong. Rushed first taps burn negative marks.
- Dead Weight — slow and wrong. A concept gap: re-learn, don't just retry.
Time Leak = time leaked on correct-but-slow solves. Greed Loss = marks lost on rushed wrong answers. Your velocity profile is your most common zone across the run.
Hack Sheets
One-page pattern tables you can print and stick on the wall — one for every Chemistry topic: Spectroscopy, Coordination Compounds, Reaction Mechanisms, Chemical Bonding, Electrochemistry, Organic Chemistry, Chemical Kinetics, Thermodynamics, Periodic Trends. The Print / Save PDF button produces a clean black-on-white sheet, nothing else.
Concept Lab
Small interactive demos that build the pattern yourself instead of memorizing it — one lab per Chemistry topic: flip the bromine coin, split the d-orbitals, call the mechanism, build a galvanic cell, and more.
Share Card
After a run, your diagnostic card appears — net score, greed loss, time traps, and your velocity profile. Download it as a PNG or share it straight to a friend.
No passwords here
There is no password. Enter your email and we send you a sign-in link — good for 30 minutes, single use. Click the link, then tap Finish signing in on the page to complete your login. Each link works on its own — requesting a new one doesn't cancel an earlier link. Can't find it? Check spam.
Sign-in is only needed for Cohort and Admin. Training needs no account.
When you're signed in you'll see a role next to your name: Student (training), Cohort (you're in a cohort — you get the velocity map), or Admin (institute admins).
Cohorts
Create a cohort or join your institute's with its code. The cohort dashboard shows the batch's velocity, greed %, concept gaps, time traps, a per-attempt scatter of time vs marks, per-topic heat, and a leaderboard on net exam economics.
Admin portal
Institute admins can roster students into a batch by pasting CSV or JSON, then watch batch telemetry — rostered vs claimed vs active students, completion, and risk flags — for their own institute's cohorts only.
What we track
First-party analytics only: per-attempt timing and aggregate counts, no keystroke capture, no ad trackers. Many of our users are students, so we keep it minimal on purpose.
Stuck?
- Link expired — request a fresh one; links are good for 30 minutes.
- Signed in but asked to sign in — sign out once, sign back in once. Still stuck, contact us below.
- Seeing a STAGING banner — you're in the test environment, not the live app. Use jee.buildfamiliar.com.
Questions? Contact us — a human reads every message.
Talk to a human
The in-app helper answers instantly and remembers what it couldn't answer. For sign-in trouble, account questions, or privacy requests, a human reads every message at support@buildfamiliar.com. Institutes: institutes@buildfamiliar.com.
Ask the helper
A rules-based assistant that answers from these same help docs — no AI guessing, and your questions are never stored. Anything it can't answer is saved for the humans to teach it.
Ask the helper
Answers come from the app's own help docs — a rules engine, not AI. It can also check your sign-in state and the app's status live. Your questions are never stored in your browser; ones it can't answer are logged (text only) so the humans can teach it.
The chat lives in the bubble at the bottom-right of every screen — always one tap away.
Sign in
One sign-in for everything: save your progress, join your institute's cohort, or manage batches as an institute admin. Training itself needs no account.
The bromine coin flip
Bromine comes in two flavors — ⁷⁹Br and ⁸¹Br — about 50/50 each. Flip a pair of bromine coins 40 times and watch the mass-spec peaks build themselves:
Two bromines give combinations (79,79), (79,81)/(81,79), (81,81) → peaks at M, M+2, M+4 in ratio 1 : 2 : 1. You don't memorize the table — you just built it. Same idea for chlorine: ³⁵Cl : ³⁷Cl is 3 : 1, so two chlorines square it → 9 : 6 : 1.
Fold the benzene
p-Dibromobenzene has a centre of symmetry: all four ring protons live identical lives → one singlet (4H) near δ 7.5. The ortho isomer is crowded and asymmetric → multiple signals. Para with different groups → two doublets (2H each).
Spectroscopy Hack Sheet
| Halogen pattern | Peaks | Ratio | Origin |
|---|---|---|---|
| 1 × Cl | M, M+2 | 3 : 1 | ³⁵Cl : ³⁷Cl ≈ 75% : 25% |
| 2 × Cl | M, M+2, M+4 | 9 : 6 : 1 | (3+1)² expansion |
| 1 × Br | M, M+2 | 1 : 1 | ⁷⁹Br : ⁸¹Br ≈ 50% : 50% |
| 2 × Br | M, M+2, M+4 | 1 : 2 : 1 | two-coin combinations |
| Benzene substitution | ¹H NMR |
|---|---|
| 1,4-disubstituted, identical groups (para) | 1 singlet, 4H |
| 1,4-disubstituted, different groups | 2 doublets, 2H each |
| 1,2-disubstituted (ortho) | multiple signals |
- Trap 1: the singlet must integrate to 4H — a 1H singlet is a different beast.
- Trap 2: low-resolution spectra can smear ortho's mess into a fake blob.
- Shortcut: read halogen counts from isotope ratios FIRST — it slaughters options before any arithmetic.
Terms of Service
Last updated: October 2026
1. Acceptance of terms
By accessing or using JEE Velocity Trainer at jee.buildfamiliar.com (the "Service"), operated by BuildFamiliar, you agree to these Terms of Service. If you do not agree, please do not use the Service.
2. What the service is
JEE Velocity Trainer is a practice and analytics app for JEE-style preparation. It offers original JEE-pattern practice questions, timed training runs, printable hack sheets, interactive concept labs, timing analytics including Time-to-Error Ratio (TER) and Exam Economics quadrant breakdowns, results history, a rules-based help assistant, and — for institutes — cohort dashboards with batch analytics. Anonymous training runs require no account; signing in unlocks saved progress, results history, and cohort membership.
3. Accounts and sign-in
Sign-in is by email magic link. Each link is valid for 30 minutes and works on its own. Login sessions last up to 30 days on the device you signed in on. Request links only for your own email address, and keep that email account secure. We may end sessions or restrict accounts that abuse the service.
4. Academic integrity
The Service is for your own practice and learning. Do not impersonate another user, misrepresent another person's work as your own, or manipulate timing or analytics.
5. Intellectual property
The question bank, hack sheets, explanations, concept labs, analytics displays, and the site's design and text are the property of BuildFamiliar and are protected by copyright. All rights reserved. You may print or save hack sheets for your personal study. No other copying, redistribution, or commercial reuse is permitted without our written permission.
6. Anti-scraping and fair use
Automated bulk scraping, unauthenticated bot extraction, and commercial redistribution of the question bank or other site content without an institutional license are prohibited. Ordinary browser use for personal study is welcome.
7. Acceptable use
Do not attempt to disrupt or overload the Service, probe other users' data, harvest credentials, or use the Service for anything unlawful.
8. Institute accounts
Institute administrators can roster students into cohorts and view analytics for their own cohort only. Access is enforced per account on our servers.
9. Availability and warranty
The Service is provided for practice and preparation, as is. We do not guarantee uninterrupted availability, and we do not promise any particular exam outcome from using it.
10. Changes to these terms
We may update these Terms; material changes will be announced in the app. Continuing to use the Service after changes take effect means you accept the updated Terms.
11. Contact
Questions about these Terms? Reach us through the contact route listed on the Help screen.
Privacy Policy
Last updated: October 2026
1. What we collect
- Account information: your email address when you sign in; your role and cohort membership if an institute assigns you one.
- Practice data: questions attempted, answers chosen, per-attempt timing, run sessions, and scores.
- Sign-in artifacts: single-use magic-link tokens (expire after 30 minutes) and login sessions (expire after 30 days).
- Support chat: Standard solved queries are not retained in user history. However, queries the helper cannot resolve are logged as anonymous text-only records so our team can improve helper coverage.
- First-party analytics: a Cloudflare Web Analytics beacon (aggregate page statistics) and per-attempt timing. We do not capture keystrokes.
2. How we use it
To run the Service: keep you signed in, show your progress and results history, compute timing analytics such as TER and Exam Economics breakdowns, provide cohort reports to institutes, and improve our question bank and content. Sign-in emails are delivered through our email provider (Resend).
3. Cohort isolation
Institute administrators can see analytics only for their own cohort. This separation is enforced on our servers, not just in the interface.
4. Storage
Data is stored on Cloudflare infrastructure: D1 for application records and KV for chat FAQ data. Data is encrypted in transit.
5. What we don't do
We do not sell your personal data. We use no third-party advertising or cross-site tracking; analytics are first-party only.
6. Retention and your choices
Magic-link tokens expire after 30 minutes; login sessions expire after 30 days. Practice history is kept while your account exists. To request a copy or deletion of your data, use the contact route listed on the Help screen.
7. Students
Many of our users are students. We collect only what the Service needs to work.
8. Changes to this policy
We may update this Policy; material changes will be announced in the app.
Cohorts for your institute
JEE Velocity Trainer gives coaching institutes a cohort dashboard: your batch's velocity, greed percentage, concept gaps, time traps, a per-attempt scatter of time vs marks, per-topic heat, and a leaderboard on net exam economics.
Institute admins roster students into a batch by pasting CSV or JSON, then watch batch telemetry — rostered vs claimed vs active students, completion, and risk flags — for their own institute's cohorts only. Analytics never cross cohort boundaries.
Cohort dashboards are set up personally by our team for pilot institutes — there is no self-serve institute signup today.
Why velocity training
JEE Velocity Trainer is a practice and analytics app for JEE Main and JEE Advanced style preparation.
The idea is simple: marks are bought with minutes. The app records how long each question takes and places every solve into one of four zones. Topper — correct and fast: the pace to hold. Time-Trap — correct but slow: hesitation is the leak, not the concept. Lucky Guess — fast and wrong: rushed first taps burn negative marks. Dead Weight — slow and wrong: a concept gap, not a speed gap.
Your most common zone across a run is your velocity profile, and your TER — target time divided by your time — tracks how efficiently you spend your minutes. Timed runs, printable hack sheets, and interactive concept labs keep the practice honest.
Our mission is to train exam temperament alongside concepts — because on exam day, velocity is half the paper.
JEE Velocity Trainer is built by BuildFamiliar.
Talk to a human
Students. Start with the in-app helper — it answers instantly from the app's own help docs, and anything it can't answer is saved for the humans to teach it. Open the chat bubble at the bottom-right of any screen.
For the rest, a human reads every message at support@buildfamiliar.com: sign-in trouble (a magic link that never arrives — check spam first), account questions, and privacy or data requests such as a copy or deletion of your data.
Institutes. Coaching institutes and training centers: institutes@buildfamiliar.com.