Which of the following is favourable condition for the formation of ionic bond ?

Which is the correct decreasing order of boiling points for different compounds from following ?

Which from following gases is least soluble in water under same conditions of temperature and pressure ?

Calculate standard Gibbs energy for any gaseous reaction if values of $K_p$ and $R$ respectively are $3.5 \times 10^{17}$ ; $8.314\,\text{JK}^{-1}\text{mol}^{-1}$