In $ 2N{O_2} \rightleftharpoons {N_2}{O_4} $
The dimerization of $ N{O_2} $ is accompanied with :
(A) decrease in paramagnetism
(B) change in color
(C) increase in temperature
(D) increase in paramagnetism

Hint: A dimer is a compound of two monomers attached by bonds that can either be strong or weak, intermolecular or covalent. Paramagnetism is a form of magnetism where some materials are weakly attracted by an externally applied magnetic field and diamagnetism is a form of magnetism where some materials are weakly repelled by an externally applied magnetic field. After dimerization, the number of unpaired electrons decreases.

Complete Step by step solution:
 $ N{O_2} $ is called nitrogen dioxide. There are five valence electrons around nitrogen. Two electrons pair with one oxygen and two electrons pair with another oxygen. 1 electron remains unpaired and this makes nitrogen dioxide paramagnetic. Nitrogen dioxide is also known as deutoxide of nitrogen. Nitrogen dioxide is one of the major atmospheric pollutants. It absorbs UV light and stops UV rays to reach onto the earth's surface. Nitrogen dioxide is a yellowish-brown liquid. Nitrogen dioxide is used as a catalyst and a nitrating agent. It is also used as an intermediate in the production of the nitric acid and sulfuric acid. Nitrogen dioxide is also used as an oxidizing agent and in the making of the explosives. Due to the unpaired electron, nitrogen dioxide is colored.
Dinitrogen tetroxide is commonly called nitrogen tetroxide. Its molecular formula is $ {N_2}{O_4} $ . Dinitrogen tetroxide is a useful reagent in chemical synthesis. Nitrogen dioxide and dinitrogen tetroxide form an equilibrium mixture. Dinitrogen tetroxide is a powerful oxidizer. The unpaired electron here pairs with a nitrogen atom. Hence paramagnetism is lost and dinitrogen tetroxide becomes diamagnetic. As there is no unpaired electron, dinitrogen tetroxide is colorless. Dinitrogen tetroxide is used to manufacture nitric oxide. During the conversion of nitrogen dioxide to dinitrogen tetroxide, paramagnetism is lost and colour is changed.
The correct answer is option A and B.

Note:
When the two monomers or the two molecules are identical, they are known as homodimers. When the two monomers or the two molecules differ, they are known as heterodimers.