Which of the following radioactive isotopes is used in the detection of thyroid cancer?

Identify the major product of the following reaction:

Two monoatomic ideal gases $1$ and $2$ of molecular masses $M_1$ and $M_2$ respectively are enclosed in separate containers kept at the same temperature. The ratio of the speed of sound in gas $1$ to that in gas $2$ is

If $\cos ^{-1}\left(\frac{x^2-y^2}{x^2+y^2}\right)=k$ (a constant),then $\frac{d y}{d x}$ is equal to

The most active phagocytic white blood cells are:

The maximum value of ${x^4}{e^{ - {x^2}}}$ is