If an object changes speed or , its velocity also changes. any change in results in acceleration.

If an object changes speed or direction, its velocity has changed. Any change in speed or direction of motion is called "acceleration".

Velocity is the vector quantity in which we need magnitude as well as the direction both.

Here we know that when we say the velocity then it means we are considering the magnitude of speed as well as direction both

Now if we say that speed is changed then in that case the velocity will also change as the magnitude of velocity is always known as speed.

So here it is correct to say that if velocity will change then it will be due to change in speed or direction of speed.

But here in both the cases we can say that acceleration may or may not be same.

because acceleration is defined as the rate of change in velocity always

so we will say

d) the number of neutrons plus the number of protons