Eight different letters of an alphabet are given. Words of four letters from these are formed. The number of such words with at least one letter repeated is :

Which of the following hormones can be used to replace vernalization?

$A$ machine gun fires a bullet of mass $40\, g$ with a velocity $1200\, m/s$. The man holding it can exert a maximum force of $144\, N$ on the gun. How many bullets can he fire per second at the most?

Below are two statements. One is labeled as Assertion $(A)$ and the other as Reason $(R).$
Assertion $(A):$ Gypsum is used to make boards for fireproof walls.
Reason $(R):$ Gypsum is unstable at high temperatures.
In the context of the above statements,choose the correct answer from the options given below:

The normal at a point on the parabola $y^2=4x$ passes through $(5,0)$. If two more normals to this parabola also pass through $(5,0)$,then the centroid of the triangle formed by the feet of these three normals is

As per the Bohr model, the minimum energy (in $eV$) required to remove an electron from the ground state of a doubly ionized $Li$ atom $(Z=3)$ is: