Which of the following compounds is consumed during the preparation of $Na_2CO_3$ by Solvay's process?

Inverted pyramid is found in

The $Adaptation$ of eyes in the dark is due to

In order to double the frequency of the fundamental note emitted by a stretched string,the length is reduced to $\frac{3}{4}$ of the original length and the tension is changed. The factor by which the tension is to be changed is

Which of the following is a biodegradable polymer?

The wavelengths of light used in an optical instrument are ${\lambda _1} = 4000\,\mathring{A}$ and ${\lambda _2} = 5000\,\mathring{A}$. The ratio of their respective resolving powers (corresponding to ${\lambda _1}$ and ${\lambda _2}$) is: