Lithium metal crystallises in a body-centred cubic $(BCC)$ crystal. If the length of the side of the unit cell of lithium is $351 \ pm$,the atomic radius of the lithium will be ............. $pm$.

If $\frac{3+2i \sin \theta}{1-2i \sin \theta}$ is a real number and $0 < \theta < 2\pi$,then $\theta$ is equal to

The $IUPAC$ name of $(CH_3)_2CH-CH_2-CH_2Br$ is

Choose the correct statement$(s)$:
$(A)$ The position of the centre of mass of a system is dependent on the choice of the coordinate system.
$(B)$ Newton's second law of motion is applicable to the centre of mass of the system.
$(C)$ Internal forces cannot change the state of the centre of mass.
$(D)$ Internal forces can change the state of the centre of mass.

$A$ small metal ball is suspended in a uniform electric field with the help of an insulated thread. If a high-energy $X-$ray beam falls on the ball,then the ball

If the area of an equilateral triangle inscribed in the circle $x^2 + y^2 + 10x + 12y + c = 0$ is $27\sqrt{3}$ sq. units,then $c$ is equal to: