Question

Among the following, the number of elements showing only one non - zero oxidation state is O, Cl, F, N, P, Sn, Tl, Na, Ti ___

Answer 1

F and Na
Only F and Na show only one non - zero oxidation state.
$O=O^{-},O^{2-},O^{2+}$;
Cl = -1 to + 7
N = -3 to +5
P = -3 to + 5
Sn = +2, +4
Tl = +1, +3 (rare but does exist)
Ti = +2, +3, +4.