12th Standard Chemistry March 2023: Online Practice Test

Explanation. Milk of Magnesia is a suspension of \(Mg(OH)_2\), a weak base that neutralises excess HCl in the stomach, so it is an antacid.

Explanation. A catalyst provides an alternative path with lower activation energy; state functions such as entropy, internal energy and enthalpy of the reaction are unchanged.

Explanation. In the Hall-Heroult process, alumina dissolved in molten cryolite is electrolysed to obtain aluminium.

Explanation. 1.73 BM = \(\sqrt{n(n+2)}\) with n = 1. \(Cu^{2+}\) is \(3d^9\) with one unpaired electron; \(Co^{2+}\) (\(d^7\), high spin) has 3, while \(Ti^{4+}\) (\(d^0\)) and square planar \([Ni(CN)_4]^{2-}\) have none.

Explanation. Butter is a gel (liquid dispersed in solid). Whipped cream is a foam, mist is an aerosol of liquid in gas, and smoke is an aerosol of solid in gas.

Explanation. HCl is a strong acid that supplies \(H^+\) ions, the ion common to the equilibrium, so it suppresses the dissociation of acetic acid.

Explanation. Each carbon in \(C_{60}\) is bonded to three other carbons in five- and six-membered rings, so it is \(sp^2\) hybridised.

Explanation. Like the lanthanoids, the actinoids most commonly show the +3 oxidation state, though they also show other states.

Explanation. DIBAL-H selectively reduces the nitrile group to an imine, which hydrolyses to the aldehyde, leaving the C=C double bond untouched. Both statements are true and the reason explains the assertion.

Explanation. Radon is radioactive and is used as a source of gamma rays (for example in radiotherapy).

Explanation. The standard electrode potential of the SHE is taken as 0 V by convention; other electrode potentials are measured against it.

Explanation. When NaCl is heated in sodium vapour, anion vacancies are occupied by electrons (F-centres), giving a metal excess defect. AgBr shows Frenkel and Schottky defects and FeO shows metal deficiency.

Explanation. DNA contains adenine, guanine, cytosine and thymine; uracil occurs only in RNA.

Explanation. Ethane-1,2-diol (ethylene glycol) lowers the freezing point of water and is used as anti-freeze in automobile radiators.

Explanation. An aromatic aldehyde condenses with a primary amine with loss of water to form an imine \(ArCH=NR\), called a Schiff's base (e.g. benzaldehyde + aniline gives benzylidene aniline).