Which of the following has the maximum tendency for hydrate formation?

Select the correct order.

Choose the correct order of acidic strength for $CO_2, CuO, CaO, H_2O$.

The electronic configuration of an element is $1s^2, 2s^2 2p^6, 3s^2 3p^3$. What is the atomic number of the element which is just below the above element in the periodic table?

The following acids have been arranged in the order of decreasing acid strength. Identify the correct order.
$I$. $ClOH$
$II$. $BrOH$
$III$. $IOH$

Which reaction is not feasible?