NEET Chemistry Practice Questions

B. Atomic number — The atomic number equals the number of protons and defines the element. The mass number is protons + neutrons.

C. Argon — Argon is a noble gas (Group 18) with a full outer electron shell, making it chemically inert. Oxygen, chlorine and nitrogen are reactive non-metals.

C. 4 — Carbon has 4 electrons in its outer shell and forms 4 covalent bonds, so its valency is 4. (6 is its atomic number, a different quantity.)

A. Red — Acids turn blue litmus red. Bases turn red litmus blue. Litmus is a common acid–base indicator.

C. Fluorine — Fluorine is the most electronegative element (about 4.0 on the Pauling scale), i.e. it attracts bonding electrons most strongly.

B. H₂O — Water is H₂O — two hydrogen atoms bonded to one oxygen atom. H₂O₂ is hydrogen peroxide and CO₂ is carbon dioxide.

A. N_A — Each CO2 molecule has 2 oxygen atoms, so 0.5 mol CO2 contains 0.5 x 2 = 1 mol of O atoms = N_A oxygen atoms.

C. n=1, l=1, m=0, s=+1/2 — For a given n, l can only take values from 0 to (n-1). With n=1, l must be 0, so l=1 is not allowed.

D. Nitrogen — Nitrogen has a half-filled 2p3 configuration, which is extra stable, so removing an electron is harder; hence IE1 of N is greater than that of O (which lies to its right).

B. sp3d2 and square planar — Xe in XeF4 has 4 bond pairs and 2 lone pairs (6 electron domains), giving sp3d2 hybridization; the two lone pairs occupy axial positions, leaving a square planar shape.

A. ΔH negative, ΔS positive — ΔG = ΔH - TΔS. When ΔH is negative and ΔS is positive, ΔG is negative at every temperature, so the reaction is spontaneous at all temperatures.

B. 3 — HCl fully dissociates, so [H+] = 0.001 = 10^-3 M, and pH = -log(10^-3) = 3.

C. +6 — Let Cr be x: 2(+1) + 2x + 7(-2) = 0, giving 2x = 12, so x = +6.

D. initial concentration of reactant — For a first-order reaction, t(1/2) = 0.693/k, which does not contain the initial concentration; hence half-life is independent of initial concentration (but depends on k, which varies with temperature and activation energy).

C. Calcium chloride — Boiling point elevation is proportional to the van't Hoff factor i. CaCl2 dissociates into 3 ions (i≈3), more than NaCl (i≈2) or the non-electrolytes glucose and urea (i=1), so it gives the greatest elevation.

A. +2 — Each K is +1 (total +4) and each CN is -1 (total -6). For neutrality: 4 + x + (-6) = 0, so x = +2.

D. HClO4 — As the oxidation state of chlorine and the number of oxygen atoms increase, the conjugate base is more stabilized by charge delocalization, so acid strength increases: HClO4 is the strongest of these oxoacids.

B. Sc3+ — Colour in transition-metal ions arises from d-d transitions. Sc3+ has a d0 configuration (empty d subshell), so no d-d transition is possible and it is colourless.

D. (CH3)3C+ (tert-butyl) — More alkyl groups attached to the positive carbon donate electron density through +I effect and hyperconjugation, stabilizing the cation. The tertiary tert-butyl cation is the most stable.

B. 3 — C5H12 has three chain isomers: n-pentane, isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane).

A. Ethanal (CH3CHO) — Tollens' reagent is reduced by aldehydes, which are oxidized to carboxylate ions, depositing a silver mirror. Ethanal is an aldehyde; ketones, alcohols, and ethers do not respond.

C. Sucrose — In sucrose the anomeric carbons of glucose and fructose are joined by the glycosidic linkage, leaving no free anomeric (hemiacetal) group, so it cannot reduce Tollens'/Fehling's reagent and is non-reducing.