From the configuration,
Metal A is Sodium or Na-2,8,1
Metal B is Calcium or Ca-2,8,8,1
Metal A i.e Sodium is more reactive than Calcium. Sodium metal reactive than calcium and it even reacts when kept open in the air.
Reaction With dil.HCl:
Sodium reacts vigorously with dilute hydrochloric acid to form sodium chlorides and hydrogen.
Calcium reacts less vigorously to form calcium chloride and hydrogen gas.
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