# Which of the following statements is not true ?

$\begin {array} {1 1} (A)\;\text{Boron is a nonmetal while all other elements of Group 13 are metal }\\ (B)\;\text{ Boron trichloride acts as a Lewis acid} \\ (C)\;\text{Boron does not form the hydrated$B^{3+}$ion} \\ (D)\;\text{ The stability of the +1 oxidation state decreases down the group whereas that of +3 increases } \end {array}$

The stability of +1 oxidation state increases down the group. This is because of the participation of only p electron. The two S - electrons $(S^2)$ do not take part in the chemical reaction ( inert pair effect ).
Hence (D) is the correct option.