Question

Which one of the following pairs of substances will not produce hydrogen when reacted together?

• A. Copper and cone. nitric acid
• B. Ethanol and metallic sodium
• C. Magnesium and steam
• D. Phenol and metallic sodium
• E. Sodium hydride and water

Answer 1

Answer: (A)

Copper, being less reactive, when reacts with cone. nitric acid, gives
$N{O}_2,$ but not $H_2$ .
$Cu+4HN{O}_3(conc)\to Cu{(N{O}_3)}_2$
$+2N{O}_2+2H_{2}O$
while $Mg$ and $NaH$
being very reactive give hydrogen gas with steam and water respectively.
$Mg+2H_{2}O\to MgO+H_2$
$NaH+H_{2}O\to NaOH+H_2$
Ethanol and phenol due to the presence of acidic hydrogen also produce hydrogen with metallic sodium.
$C_2{H}_{5}OH+Na\to C_2{H}_5{O}^{-}N{a}^{+}+H_2$
$C_6{H}_{5}OH+Na\to C_6{H}_5{O}^{-}N{a}^{+}+H_2$