The specific resistance (resistivity) of material $B$ is twice that of material $A$. The diameter of a circular wire made of $B$ is twice that of a wire made of $A$. If the resistances of both wires are equal,then the ratio of their lengths $l_B/l_A$ will be .......

What is the gametophytic stage of Pteridophytes?

$A$ compound $(A)$ is used in the preparation of washing soda to recover ammonia in the Solvay process. When $CO_2$ is bubbled through an aqueous solution of $(A)$,the solution turns milky. It is also used in whitewashing due to its disinfectant nature. What is the chemical formula of $(A)$?

From which part is clove oil extracted?

$A$ ray of light of intensity $I$ is incident on a parallel glass slab at point $A$ as shown in the diagram. It undergoes partial reflection and refraction. At each reflection, $25\%$ of incident energy is reflected. The rays $AB$ and $A'B'$ undergo interference. The ratio of $I_{max}$ and $I_{min}$ is (in $: 1$)

Anhydrous $Na_2CO_3$ is also known as