If a polygon of $n$ sides has $275$ diagonals,then $n$ is equal to

Which one of the following plots is correct for a first order reaction?

The enzyme enterokinase helps in the conversion of $............$.

In $Ulothrix$,$Spirogyra$,and $Chlamydomonas$,at what stage does meiosis occur?

$A$ tower subtends angles $\alpha, 2 \alpha$ and $3 \alpha$ respectively at points $A, B$ and $C$,all lying on a horizontal line through the foot of the tower. Then $\frac{A B}{B C}$ is equal to:

Identify the correct gland on the basis of the following characteristics:
$(I)$ It is located on the dorsal side of the forebrain.
$(II)$ It plays a very important role in the regulation of the $24$-hour rhythm of our body.
$(III)$ It helps in maintaining the body temperature.
$(IV)$ Its hormone influences metabolism as well as defense capability.