On the Earth,a stone is thrown from a height in a direction parallel to the Earth's surface,while another stone is simultaneously dropped from the same height. Which stone would reach the ground first and why?

(NONE) Both stones will reach the ground at the same time. This is because the vertical motion of both stones is governed by the same gravitational acceleration $(g)$ and they are released from the same initial height $(h)$. The horizontal velocity imparted to the first stone does not affect its vertical motion or the time taken to fall under gravity,as described by the equation of motion $h = \frac{1}{2}gt^2$,where $t = \sqrt{\frac{2h}{g}}$.