JEE Main · ChemistryHard

$Consider the thermal decomposition of group 2 metal nitrates M (NO_{3})_{2} . Which of the following statements correctly describes the trend in the decomposition temperature and the products formed?$

A. $Decomposition temperature increases down the group and all form metal nitrites and oxygen.$
B. $Decomposition temperature increases down the group and all form metal oxides, NO_{2}, and O_{2} .$
C. $Decomposition temperature decreases down the group and all form metal oxides, NO_{2}, and O_{2} .$
D. $Decomposition temperature increases down the group and only Be (NO_{3})_{2} forms the metal oxide.$

Show correct answer & step-by-step solution

Correct answer: B — $Decomposition temperature increases down the group and all form metal oxides, NO_{2}, and O_{2} .$

Solution

$The thermal stability of group 2 nitrates increases down the group as the polarizing power of the cation M^{2 +} decreases.$
$All group 2 nitrates decompose according to the reaction: 2 M (NO_{3})_{2} Δ 2 MO + 4 NO_{2} + O_{2} .$
$The decomposition temperature increases as the ionic character of the metal-oxygen bond increases down the group.$
$Hence the answer is (B).$

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