JEE doubts
700 doubts found
I keep getting “Saturation” questions wrong in Hydrocarbons. What's the trap?
thinking unsaturated hydrocarbons are less reactive than alkanes.
Why does putting salt in pasta water or antifreeze in a car radiator change the boiling/freezing point?
Both are colligative effects.
Why can metals be hammered into sheets and conduct electricity, while an ionic crystal like salt just shatters?
A metal is a lattice of positive ions in a 'sea' of delocalised electrons; when you hammer it, layers slide but the electron sea keeps holding them together, so it bends and flattens, and those mobile electrons carry current.
Why do aerosol and deodorant cans warn 'do not heat or incinerate'?
At fixed volume, a gas's pressure rises in direct proportion to its absolute temperature (Gay-Lussac's law, P ∝ T).
How do chelating agents like EDTA treat heavy-metal (lead) poisoning?
EDTA is a polydentate ligand that wraps around a metal ion at six points, forming a very stable, water-soluble chelate ring.
Why were CFCs banned for damaging the ozone layer?
Chlorofluorocarbons are so unreactive they drift up to the stratosphere intact.
Why does ethanol mix with water in all proportions, but oil-like higher alcohols don't?
Ethanol's small O–H group hydrogen-bonds strongly with water, and its tiny carbon chain barely gets in the way, so the two mix completely.
Why are aldehydes generally more reactive than ketones towards nucleophiles?
The carbonyl carbon is the reactive spot, and two effects make aldehydes more open to attack.
Why is aniline a much weaker base than methylamine?
Basicity depends on how available the nitrogen's lone pair is to grab a proton.
What does “Molar mass” actually mean in Some Basic Concepts (Mole Concept), and why does it matter for JEE?
the mass of one mole of a substance in grams, numerically equal to its atomic/molecular mass.
What does “Orbitals” actually mean in Structure of Atom, and why does it matter for JEE?
regions around the nucleus where an electron is most likely to be found (s spherical, p dumbbell).
What does “VSEPR theory” actually mean in Chemical Bonding & Molecular Structure, and why does it matter for JEE?
electron pairs around a central atom arrange to be as far apart as possible, fixing the molecule's shape.
What does “Entropy (S)” actually mean in Chemical Thermodynamics, and why does it matter for JEE?
a measure of disorder or the number of ways energy can be arranged.
What does “Le Chatelier's principle” actually mean in Equilibrium, and why does it matter for JEE?
if you disturb a system at equilibrium, it shifts to oppose the change.
What does “Oxidation number” actually mean in Redox Reactions, and why does it matter for JEE?
a bookkeeping charge assigned by rules to track electron transfer.
What does “Ionization energy” actually mean in Periodic Table & Periodicity, and why does it matter for JEE?
the energy to remove the outermost electron; it rises across a period and falls down a group.
What does “Rate constant” actually mean in Chemical Kinetics, and why does it matter for JEE?
the proportionality constant k in the rate law; it rises sharply with temperature.
What does “Anode and cathode” actually mean in Electrochemistry, and why does it matter for JEE?
oxidation always happens at the anode and reduction always at the cathode.
What does “Resonance” actually mean in Organic Chemistry — Basic Concepts, and why does it matter for JEE?
delocalisation of electrons over several atoms, giving extra stability.
What does “Markovnikov's rule” actually mean in Hydrocarbons, and why does it matter for JEE?
when HX adds to an alkene, H attaches to the carbon that already has more hydrogens.
Why do raisins swell up in water but a cucumber shrivels into a pickle in brine?
It's osmosis, driven by the concentration difference across the cell membranes.
Why does window glass have no fixed melting point and can even slowly 'flow' over centuries?
Glass is amorphous — its particles are frozen in a disordered, liquid-like arrangement rather than a neat crystal lattice.
Why do scuba divers get 'the bends' if they surface too quickly?
Gas solubility rises with pressure (Henry's law).
Why is haemoglobin so good at carrying oxygen, and why is carbon monoxide so deadly?
Haemoglobin holds an Fe²⁺ ion in a porphyrin ring; oxygen binds reversibly to this iron centre as a ligand, so blood can pick up O₂ in the lungs and release it in the tissues.