Chemistry MCQs for NEET — Practice Questions with Answers

Referring to Table 3.4 'Notation for IUPAC nomenclature of Elements': Oct-o, Enn-e, and Quad-q are all correctly matched. Therefore, 'All of the above' is the correct answer.

The NCERT text states: 'For example, both American and Soviet scientists claimed credit for discovering element 104. The Americans named it Rutherfordium whereas Soviets named it Kurchatovium.'

Un (u) + un (u) + quad (q) = Uuq. This is the symbol for Ununquadium (Z=114), as listed in Table 3.5.

For Z=107, the roots are un (1), nil (0), sept (7). Combining these with the 'ium' suffix gives Unnilseptium. Table 3.5 confirms that Bohrium is the official name for Unnilseptium (Z=107).

According to Table 3.4 'Notation for IUPAC nomenclature of Elements', the numerical root for the digit '0' is 'nil'.

According to the NCERT text, 'C— Cl bond acquires a partial double bond character due to resonance. As a result, the bond cleavage in haloarene is difficult than haloalkane and therefore, they are less reactive towards nucleophilic substitution reaction.' Also, 'The sp2 hybridised carbon with a greater s-character is more electronegative and can hold the electron pair of C— X bond more tightly than sp3-hybridised carbon in haloalkane with less s-chararcter. Thus, C— Cl bond length in haloalkane is 177pm while in haloarene is 169 pm. Since it is difficult to break a shorter bond than a longer bond, therefore, haloarenes are less reactive than haloalkanes towards nucleophilic substitution reaction.'

The NCERT states, 'The presence of an electron withdrawing group (-\text{NO}_2) at ortho- and para-positions increases the reactivity of haloarenes.' It further explains, 'As shown, the presence of nitro group at ortho- and para-positions withdraws the electron density from the benzene ring and thus facilitates the attack of the nucleophile on haloarene. The carbanion thus formed is stabilised through resonance.'

The NCERT text mentions, 'Halogen atom besides being slightly deactivating is o, p -directing; therefore, further substitution occurs at ortho- and para-positions with respect to the halogen atom.' It also states, 'Further , the halogen atom because of its –I effect has some tendency to withdraw electrons from the benzene ring. As a result, the ring gets somewhat deactivated as compared to benzene and hence the electrophilic substitution reactions in haloarenes occur slowly and require more drastic conditions as compared to those in benzene.'

The NCERT specifies, 'The effect is pronounced when (-NO2) group is introduced at ortho- and para- positions. However, no effect on reactivity of haloarenes is observed by the presence of electron withdrawing group at meta-position.' This indicates that a nitro group at the ortho-position would increase reactivity.

The NCERT states, 'The sp2 hybridised carbon with a greater s-character is more electronegative and can hold the electron pair of C— X bond more tightly than sp3-hybridised carbon in haloalkane with less s-chararcter. Thus, C— Cl bond length in haloalkane is 177pm while in haloarene is 169 pm.'