Chemistry MCQs for NEET — Practice Questions with Answers

The text highlights, 'The importance of the third law lies in the fact that it permits the calculation of absolute values of entropy of pure substance from thermal data alone.'

The context explains, 'Mol ecules of a substance may move in a straight line in any direction, they may spin like a top and the bonds in the molecules may stretch and compress. These motions of the molecule are called translational, rotational and vibrational motion respectively.' Spinning like a top corresponds to rotational motion.

The text states, 'When temperature of the system rises, these motions become more vigorous and entropy increases.'

According to Problem 5.10 (ii) and its solution, 'At 0 K, the constituent particles are static and entropy is minimum. If temperature is raised to 115 K, these begin to move and oscillate about their equilibrium positions in the lattice and system becomes more disordered, therefore entropy increases.'

The text mentions, 'theoretical arguments and practical evidences have shown that entropy of solutions and super cooled liquids is not zero at 0 K.' This implies they lack the 'perfect order' characteristic of a pure crystalline solid at absolute zero, retaining some residual disorder (multiple microstates).

The text describes 'translational, rotational and vibrational motion' as contributing to entropy. Nuclear motion is not mentioned in this context.

The text explicitly states, 'On the other hand when temperature is lowered, the entropy decreases.'

The text states, 'Therefore, increase in entropy in such systems is the natural direction of a spontaneous change. This, in fact is the second law of thermodynamics.'

According to the provided context, o-Cresol has the IUPAC name 2-Methylphenol. Ortho- (o-) indicates substituents at positions 1 and 2, and since phenol is the parent, the methyl group is at the 2-position.

Ethers are classified as simple or symmetrical if the alkyl or aryl groups attached to the oxygen atom are the same, and mixed or unsymmetrical if the two groups are different. In $\\text{C}_2\\text{H}_5\\text{OCH}_3$, the groups are ethyl and methyl, which are different, making it an unsymmetrical ether. $\\text{CH}_3\\text{OCH}_3$ and $\\text{C}_2\\text{H}_5\\text{OC}_2\\text{H}_5$ are symmetrical ethers. $\\text{C}_6\\text{H}_5\\text{OCH}_3$ is also an unsymmetrical ether, but the question asks 'which of the following', and $\\text{C}_2\\text{H}_5\\text{OCH}_3$ is explicitly mentioned as an example of an unsymmetrical ether in the text.