Which force acts on a body first: action or reaction?

Which parameter is used to determine the effect of force on a body?

$A$ force of $50 \, dynes$ acts on a particle of mass $5 \, g$ for $3 \, seconds$. What is the impulse of the force?

$A$ ball of mass $3 \ kg$ strikes a wall at an angle of $60^\circ$ with a velocity of $10 \ m/s$ and rebounds at the same angle and speed. What is the change in momentum of the ball in $MKS$ units?

Two billiard balls each of mass $0.05\; kg$ moving in opposite directions with speed $6\; m/s$ collide and rebound with the same speed. What is the impulse imparted to each ball due to the other (in $; Ns$)?

$A$ ball of mass $150\,g$ starts moving with an acceleration of $20\,m/s^2$. When hit by a force,which acts on it for $0.1\,s$. The impulsive force is ........ $N-s$.