A stone dropped from the top of the tower touches the ground in 4 sec. The height of the tower is about

To find the height of the tower, we can use the equations of motion under gravity.

When a stone is dropped from the top of a tower, its initial velocity ($u$) is zero:
$u=0\text{m/s}$

The time taken ($t$) by the stone to reach the ground is:
$t=4\text{s}$

The acceleration acting on the stone is the acceleration due to gravity ($g$), which is approximately:
$g\approx 10{\text{m/s}}^2$ (or more precisely $9.8{\text{m/s}}^2$)

Using the second equation of motion to calculate the distance travelled (height of the tower, $h$):
$h=ut+\frac{1}{2}g{t}^2$

Substitute the values into the equation:
$h=\left(0\right)\left(4\right)+\frac{1}{2}\left(10\right){\left(4\right)}^2$

Simplify the expression:
$h=0+5\times 16$
$h=80\text{m}$

Therefore, the height of the tower is about 80 m, which corresponds to the correct option.