1. at which point is the vertical velocity equal to zero? 2.during which part of the projectile's path does velocity increase?

#1

in projectile motion when object reached to the highest point then its velocity in vertical direction becomes zero

So its velocity in vertical direction is zero at POINT B

#2

During first half part of motion ball goes up high in air so its vertical speed will decrease due to gravity

while when it will drop back in next half where its vertical speed will increase

So its speed will increase between point B and C

d is the correct answer