Which ion has the maximum complex-forming tendency?

An element $P$ has atomic number $56$. What will be the formula of its halide?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Barium carbonate is insoluble in water and is highly stable.
Reason $R$: The thermal stability of the carbonates increases with increasing cationic size.
Choose the most appropriate answer from the options given below for $A$ and $R$.

Which element from the following exhibits a common oxidation state of $+2$?

The property of the alkaline earth metals that increases with their atomic number is

$A$ hydrated colorless solid $(A)$ is water soluble and finds use in medicine as a purgative. When a solution of $(A)$ is treated with ammonium phosphate,a white precipitate is formed. $(A)$ gives a pink mass in the cobalt nitrate cavity test. What is $(A)$?