Which of the following alkaline earth metals forms complex salts?

The element having atomic number $56$ belongs to

Assertion $A$: Barium is not required in the normal biochemical processes of the human body.
Reason $R$: Barium does not exhibit more than one oxidation state.

$(a)$ Give reactivity of alkaline earth metals towards air,water,dihydrogen and acids.
$(b)$ Explain reducing nature of alkaline earth metals.
$(c)$ Give chemical reaction of alkaline earth metals with liquid ammonia.

The number of water molecules in gypsum and plaster of paris respectively are

Which of the following on thermal decomposition gives both basic and acidic oxides?