Which of the following noble gases does not have an octet of electrons in its outermost shell?

In which of the following reactions is the product an ether?

$A$ given mass of a gas is compressed isothermally until its pressure is doubled. It is then allowed to expand adiabatically until its original volume is restored and its pressure is then found to be $0.75$ of its initial pressure. The ratio of the specific heats of the gas is approximately :

The oxoacid of sulphur which contains two sulphur atoms in different oxidation states is

If the volume of a sphere increases at the rate of $2 \pi \text{ cm}^3/\text{s}$, then the rate of increase of its radius (in $\text{cm/s}$), when the volume is $288 \pi \text{ cm}^3$, is

$A$ steel rod $100 \, cm$ long is clamped at its middle. The fundamental frequency of longitudinal vibrations of the rod is $2.53 \, kHz$. What is the speed of sound in steel in $km/sec$?