If $x=\log _{0.1} 0.001$ and $y=\log _9 81$,then $\sqrt{x-2 \sqrt{y}}$ is equal to

If in a $\triangle ABC$,$\frac{1}{a+c} + \frac{1}{b+c} = \frac{3}{a+b+c}$,then $\angle C$ is equal to (in $^{\circ}$)

Particles of masses $m, 2m, 3m, \dots, nm$ grams are placed on the same line at distances $l, 2l, 3l, \dots, nl$ cm from a fixed point. The distance of the centre of mass of the particles from the fixed point in centimetres is:

Which set of elements forms stable,covalently bonded hydrogen-bonded hydrides?

Which tissue is mainly composed of fat-storing cells?

$A$ light wave enters from medium $1$ to medium $2$. Its velocity in the $2^{\text{nd}}$ medium is double that in the $1^{\text{st}}$ medium. For total internal reflection,the angle of incidence must be greater than ....... $^{\circ}$.