The activity of a radioactive sample is measured as $N_0$ counts per minute at $t = 0$ and $N_0/e$ counts per minute at $t = 5$ minutes. The time (in minutes) at which the activity reduces to half its value is

Among the following compounds,which one is not responsible for the depletion of the ozone layer?

$A$ cylindrical metallic rod,in thermal contact with two heat reservoirs at its two ends,conducts an amount of heat $Q$ in time $t$. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. The amount of heat conducted by the new rod,when placed in thermal contact with the same two reservoirs in time $t$,is:

When a system is taken from state $i$ to state $f$ along the path $iaf,$ it is found that $Q = 50 \, cal$ and $W = 20 \, cal$. Along the path $ibf$,$Q = 36 \, cal$. Work done along the path $ibf$ will be ........... $cal$.

If $n(A) = 3$,$n(B) = 6$ and $A \subseteq B$,then the number of elements in $A \cup B$ is:

The work of $146 \, kJ$ is performed in order to compress one kilo mole of a gas adiabatically,and in this process,the temperature of the gas increases by $7 \, ^oC$. The gas is $(R = 8.3 \, J \, mol^{-1} \, K^{-1})$.