Question

The metals A and B form oxide but B also forms nitride when both burn in air. The A and B are
(a) Cs, K
(b) Mg, Ca
(c) Li, Na
(d) K, Mg

Answer 1

Answer : option(b)...

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Answer 2

OPTION (d) IS CORRECT.

(d) K, Mg

Explanation:

• When a metal is burnt in air it forms an oxide, but some elements form nitrides as well.
• The element Cesium forms oxide very rarely. Magnesium, lithium, and potassium forms stable oxides.
• Elements like calcium, sodium, potassium do not form stable nitrides. So, their nitrides will not be present in air.
• So, element A can be Mg, Li, or K but element B can only be Mg. So, this means that option (a), (b) and (c) can not be the right answer.
• Therefore, option (d) is correct.

      $2K+O_{2} --> K_{2}O\\2Mg+O_{2}-->2MgO\\3Mg+N_{2}-->Mg_{3}N_{2}$