Answer:
m = 3.75 [kg]
Explanation:
We must remember that momentum is defined as the product of mass by Velocity, therefore it can be represented by means of the following equation.

where:
P = momentum = 93.75 [kg*m/s]
m = mass [kg]
v = velocity = 25 [m/s]
Now replacing, we can clear the mass:
![P=m*v\\m=P/v\\m=93.75/25\\m=3.75 [kg]](https://tex.z-dn.net/?f=P%3Dm%2Av%5C%5Cm%3DP%2Fv%5C%5Cm%3D93.75%2F25%5C%5Cm%3D3.75%20%5Bkg%5D)
I've had a similar question on an assignment myself, so I'm going to assume it had the same idea.
When you organize them in such a way, the pattern that emerges tells you elements organized by atomic weight have the same number of valence electrons.
Hope this helps!
Answer: The answer is D: 300,000km/s
Explanation: