In case of stationary wave pattern, which of the following statement is CORRECT ?

Out of the following musical instruments which is ' NOT ' a percussion instrument?

The enclosed air inside a closed box of rigid walls has pressure $P_1$. The density of air inside this box is constant. On heating the gas, the pressure of the enclosed air is increased from $P_1$ to $P_2$. Now it is observed that the sound travels $1.4$ times faster than at pressure $P_1$. The ratio $P_2$ by $P_1$ is

Select the WRONG statement about polar molecules.