Choose the correct statement from the following.

I. In vapour phase $\mathrm{BeCl}_2$ exists as chlorobridge dimer.

II. $\mathrm{BeSO}_4$ is readily soluble in water.

III. BeO is completely basic in nature.

IV. $\mathrm{BeCO}_3$ being unstable, is kept in the atmosphere of $\mathrm{CO}_2$.

V. $\mathrm{BeCO}_3$ is less soluble among all the carbonates of group 2 elements.

Identify the compound which gives $\mathrm{CO}_2$ more readily on heating?

What is the correct stability order of $\mathrm{KO}_2, \mathrm{RbO}_2, \mathrm{CsO}_2$ ?

Assertion (A) $\mathrm{MgO}, \mathrm{CaO}, \mathrm{SrO}$ and BaO are insoluble in water.

Reason ( R ) In aqueous medium the basic strength of $\mathrm{MgO}, \mathrm{CaO}, \mathrm{SrO}$ and BaO increases with increase in the atomic number of metal.

The correct option among the following is