Which of the following will be the most stable diazonium salt R{N_2}^ + {X^ - } ?(A) C{H_3}{N_2}^ + {X^ - }(B) {C_6}{H_5}{N_2}^ + {X^ - }(C) C{H_3}C{H_2}{N_2}^ + {X^ - }(D) {C_6}{H_5}C{H_2}{N_2}^ + {X^ - }

The stability of diazonium salts depends on the nature of the substituents attached to the nitrogen atom. Generally, electron-donating groups stabilize diazonium salts by delocalizing the positive charge through resonance, while electron-withdrawing groups destabilize them.

Among the given options:

(A) CH3N2+X-: The methyl group is electron-donating, so it would stabilize the diazonium ion.

(B) C6H5N2+X-: The phenyl group is electron-donating through resonance, so it would stabilize the diazonium ion more than a simple alkyl group like methyl.

(C) CH3CH2N2+X-: The ethyl group is also electron-donating, albeit less than a methyl group, so it would still contribute to the stability of the diazonium ion.

(D) C6H5CH2N2+X-: This compound has both a phenyl group and an ethyl group. The phenyl group would contribute significantly to stabilizing the ion through resonance, but the ethyl group would contribute less compared to a methyl group.

Considering the above analysis, option (B) C6H5N2+X- would likely be the most stable diazonium salt because the phenyl group is a strong electron-donating group that can stabilize the positive charge through resonance. So, the answer is (B).