Chemistry MCQs for NEET — Practice Questions with Answers

The NCERT states, 'For example, lithium unlike other alkali metals... form compounds with pronounced covalent character; the other members of these groups predominantly form ionic compounds.' Therefore, Liâ‚‚O would exhibit more covalent character compared to Naâ‚‚O, which is predominantly ionic.

The NCERT states that 'lithium unlike other alkali metals, and beryllium unlike other alkaline earth metals, form compounds with pronounced covalent character'. This anomalous behavior, including covalent character, is attributed to their 'small size, large charge/radius ratio and high electronegativity'.

The text states, 'the first member of group has only four valence orbitals (2s and 2p) available for bonding'. This means that second-period elements cannot expand their octet, thus restricting their maximum covalency to four (one s and three p orbitals). The absence of d-orbitals prevents higher covalency.

According to the NCERT, 'The anomalous behaviour is attributed to their small size, large charge/radius ratio and high electronegativity of the elements.' These factors lead to a greater tendency for covalent bonding in second-period elements compared to their heavier group members (Y), which tend to form more ionic compounds due to larger size and lower electronegativity. Atomic radius increases down a group, and electronegativity decreases down a group. Second-period elements have fewer valence orbitals (2s, 2p) than third-period elements (3s, 3p, 3d, where 3d orbitals can be utilized).

According to the NCERT text, 'Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide.' This is the correct initial step in the industrial preparation of phenol from cumene.

The NCERT states, 'Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids.' Hydrolysis is the reaction with water that breaks a bond.

The NCERT states, 'Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced.' These harsh conditions are characteristic of the Dow's process.

NCERT states 'From benzenesulphonic acid: Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.'

In methods like the one from benzenesulphonic acid or haloarenes, sodium phenoxide is formed. Acidification (e.g., with dilute acid) is used to protonate the phenoxide ion ($C_6H_5O^-$) to regenerate the neutral phenol ($C_6H_5OH$). The NCERT states, 'Acidification of the sodium salt gives phenol.'

The NCERT text specifies, 'A diazonium salt is formed by treating an aromatic primary amine with nitrous acid ($NaNO_2 + HCl$) at 273-278 K.' This low temperature range (0-5 °C) is crucial for the stability of diazonium salts.