In which of the following pairs,the central atoms have the same number of lone pairs of electrons?

The wavelengths of two sound notes in air are $\frac{40}{195} ~m$ and $\frac{40}{193} ~m$. Each note produces $9$ beats per second separately with a third note of fixed frequency. The velocity of sound in air in $m/s$ is

Three waves of equal frequency having amplitudes $10 \mu m,$ $4 \mu m,$ and $7 \mu m$ arrive at a given point with a successive phase difference of $\frac{\pi}{2}.$ The amplitude of the resulting wave in $\mu m$ is given by

Which of the following pairs of elements cannot form an alloy?

The spleen is a:

The force required to move a body up a rough inclined plane is double the force required to prevent the body from sliding down the plane. The coefficient of friction,when the angle of inclination of the plane is $60^{\circ}$,is