Question

Which of the following cannot be used to generate hydrogen gas?

• A. $Al+NaOH$
• B. $Zn+NaOH$
• C. $Mg+NaOH$
• D. $LiH+H_{2}O$

Answer 1

Answer: (C)

$Mg+NaOH$

$Mg+NaOH$ cannot be used to generate hydrogen gas.

The reactions leading to generation of hydrogen gas are as follows:
(A) $2Al+2NaOH+2H_{2}O\to \underset{\text{sodium meta aluminate}}{2NaAl{O}_2}+3H_2\uparrow$
(B) $Zn+2NaOH\to N{a}_{2}Zn{O}_2+H_2$
(C) $Mg$ is not affected by alkalies. Hence, it does not react with $NaOH$.
(D) $LiH+H_{2}O\to H_2\uparrow +LiOH$

Hence, option C is correct.