The idea of secondary wavelets for the propagation of a wave was first given by

The spectrum of a black body at two temperatures $27^oC$ and $327^oC$ is shown in the figure. Let $A_1$ and $A_2$ be the areas under the two curves respectively. The value of $\frac{A_2}{A_1}$ is

Aqueous solutions of two compounds $M_1-OH$ and $M_2-OH$ are prepared in two different beakers. If the electronegativity of $M_1 = 3.4, M_2 = 1.2, O = 3.5$ and $H = 2.1$,then the nature of the two solutions will be respectively:

$A$ sample of a radioactive element has a mass of $10 \, g$ at an instant $t = 0$. The approximate mass of this element in the sample after two mean lives is ........ $g$.

Reserpine is obtained from ...... .

What is the volume (in litres) of oxygen at $STP$ required for complete combustion of $32 \ g$ of $CH_4$ ? (Molecular weight of $CH_4$ is $16$ )