This is what scientists call newton's cradle. it is a handy devise used to illustrate many concepts in physics.
imagine the ball on the right is dropped. according to newton's third law of motion, what is the expected
result once the ball hits the ball closest to it?
the single ball on the left will move as high as the ball on the right
was dropped.
the dropped ball will exert a force on the first ball it hits and that
ball will move slightly.
the second ball will move to the right causing a chain reaction and
all four balls will then move right.
the second ball in the line will exert and equal force on the dropped
ball and both balls will stop moving.

According to Newton's third law of motion, "The single ball on the left will move as high as the ball on the right  was dropped" is the expected  result once the ball hits the ball closest to it.

Option A

Explanation:

Newton’s cradle is the best example for law of conservation of momentum. So that means that energy or momentum exhibited by a particle can be transferred to its nearer object with equal force. So in the given options the first option is correct. As when the right ball is dropped it will collide with its neighboring ball and transfer energy.

By this transferring of energy from one particle to another, it will reach the leftmost ball. But there will be no loss in the energy as the left ball will move as high position as the ball on the right was dropped from. So that means the energy is conserved in the cradle.

what was the answer?

the bal will not change its velocity.