You can find the mass of an atom by adding the number of protons and neutrons. In this case the atom has 2 protons and 3 neutrons so the mass is 5.

Actually Welcome to the Concept of the Projectile Motion.
Since, here given that, vertical velocity= 50m/s
we know that u*sin(theta) = vertical velocity
so the time taken to reach the maximum height or the time of Ascent is equal to
T = Usin(theta) ÷ g, here g = 9.8 m/s^2
so we get as,
T = 50/9.8
T = 5.10 seconds
thus the time taken to reach max height is 5.10 seconds.
Answer: b. The combination is a mixture because the substances can be separated
Explanation: Based on the facts presented above, the combination of both both substances can be referred to as a mixture due to the following:
A mixture is obtained when two or more substances or materials are combined without a chemical reaction. This is observed when Jalen combined substance 1 and 2 with only one of the substances becoming visible after the combination.
The other reason is that, a mixture can be separated back into its original constituent, this is evident when the combination was filtered with only substance 2 going through the filter and substance 1 remaining in the filter