From which of the following minerals is $Ra$ (Radium) obtained?

What is the molecular formula of borazole?

If $x$ and $y$ are acute angles such that $\cos x + \cos y = \frac{3}{2}$ and $\sin x + \sin y = \frac{3}{4}$,then $\sin(x+y)$ is equal to

$A$ light string passing over a smooth light pulley connects two blocks of masses $m_1$ and $m_2$ (vertically). If the acceleration of the system is $(\frac{g}{8})$,then the ratio of masses $m_2 : m_1$ is:

The driver of a car travelling with speed $30 \,m/s$ towards a hill sounds a horn of frequency $600 \,Hz$. If the velocity of sound in air is $330 \,m/s$,the frequency of reflected sound as heard by the driver is ........ $Hz$.

Two circular coils $X$ and $Y$,having an equal number of turns,carry equal currents in the same sense and subtend the same solid angle at point $O$. If the smaller coil $X$ is midway between $O$ and $Y$,and if we represent the magnetic induction due to the bigger coil $Y$ at $O$ as $B_Y$ and that due to the smaller coil $X$ at $O$ as $B_X$,then $\frac{B_Y}{B_X}$ is