Question

What happens when magnesium is burnt in air and the products $X$ and $Y$ are treated with water ?

	$X$	$Y$	$P$	$Q$
(a)$\,\,$	$MgO\,\,$	$Mg(OH)_2\,\,$	$Mg(OH)_2\,\,$	$N_2\,\,$
(b)$\,\,$	$MgO\,\,$	$Mg_3N_2\,\,$	$Mg(OH)_2\,\,$	$NH_3\,\,$
(c)$\,\,$	$MgO\,\,$	$Mg_3N_2\,\,$	$Mg(OH)_2\,\,$	$N_2\,\,$
(d)$\,\,$	$MgO\,\,$	$MgCO_3\,\,$	$Mg(OH)_2\,\,$	$CO_2$

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

Magnesium reacts with air to form oxide and nitride. On reaction with water the oxide gives hydroxide and nitride gives hydroxide and ammonia.
$2Mg +O_2 \rightarrow \underset{(X)}{2MgO}$
$3Mg +N_2 \rightarrow \underset{(Y)}{Mg_3N_2}$
$MgO +H_2O \rightarrow \underset{(P)}{Mg(OH)_2}$
$MgO +H_2O \rightarrow \underset{(P)}{3Mg(OH)_2}+\underset{(Q)}{2NH_3}$