The $24$ hour (diurnal) rhythm of our body,such as the sleep-wake cycle,is regulated by the hormone:

Which of the following is not an antibiotic?

Which one of the following equations is correct for the reaction $N_{2(g)} + 3H_{2(g)} \longrightarrow 2NH_{3(g)}$?

The extension in a string,obeying Hooke's law,is $x$. The speed of sound in the stretched string is $v$. If the extension in the string is increased to $1.5x$,the speed of sound will be (in $, v$)

If ${a^{x - 1}} = bc$,${b^{y - 1}} = ca$,and ${c^{z - 1}} = ab$,then find the value of $\sum \frac{1}{x}$.

Identify from the following,a plant tissue in which lignin does not occur in the cell walls?