The molecular formula of diphenylmethane is $C_{13}H_{12}$. How many structural isomers are possible when one hydrogen atom is replaced by a chlorine atom?

In Young's double slit experiment,if the maximum intensity is $I$,then the angular position where the intensity becomes $\frac{I}{4}$ is:

The engine of a jet aircraft applies a thrust force of $10^5 \ N$ during take-off and causes the plane to attain a velocity of $1 \ km/s$ in $10 \ s$. The mass of the plane is:

$A$ metallic wire with tension $T$ and at temperature $30^{\circ} C$ vibrates with its fundamental frequency of $1 \ kHz$. The same wire with the same tension but at $10^{\circ} C$ temperature vibrates with a fundamental frequency of $1.001 \ kHz$. The coefficient of linear expansion of the wire is

Hydrogen behaves as an oxidising agent when it reacts with

Let $n = 1! + 4! + 7! + \ldots + 400!$. Then the ten's digit of $n$ is