Question

Which of the following combination will produce $H_2$ gas?

• A. $Au$ metal and $NaCN\left(aq\right)$ in the presence of air
• B. $Cu$ metal and $conc.HN{O}_3$
• C. $Fe$ metal and $conc.HN{O}_3$
• D. $Zn$ metal and $NaOH\left(aq\right)$

Answer 1

The correct option is D $Zn$ metal and $NaOH\left(aq\right)$

Zn metal and NaOH(aq) will produce hydrogen gas.
$Zn+2NaOH\to N{a}_{2}Zn{O}_2+H_2\uparrow$
Gold react with sodium cyanide, oxygen and water, but no hydrogen gas is obtained.
$4Au+8NaCN+O_2+2H_{2}O\to 4Na\left[Au\right(CN{)}_2]+4NaOH$
Cu metal reacts with conc. nitric acid but no hydrgen gas is obtained.
$Cu+4HN{O}_3\to Cu(N{O}_3{)}_2+2H_{2}O+2N{O}_2\uparrow$
Fe metal reacts with conc. nitric acid but no hydrgen gas is obtained.
$Fe+6HN{O}_3\to Fe(N{O}_3{)}_3+3H_{2}O+3N{O}_2\uparrow$

Hence, the correct option is D.