Thank you for reporting, we will resolve it shortly
Q.
At the maximum height of a projectile, the velocity and acceleration are
Motion in a Plane
Solution:
At maximum height ;
$v _{ x }= v _{ x } \cos \theta$ in horizontal direction and $v _{ y }=0$
$
a _{ x }=0, a _{ y }=- g
$
Clearly angle between them is $90^{\circ}$.