Answer:
is missing
Explanation:
In a nuclear reaction, the total mass and total atomic number remains the same.
For the given reaction:

To calculate A:
Total mass on reactant side = total mass on product side
4 + 9 = 12 + A
A = 1
To calculate Z:
Total atomic number on reactant side = total atomic number on product side
2 + 4 = 6 + Z
Z = 0

Hence, missing is
.
The pressure will not affect the rate of solution.
B because they are in the same periodic table group
I believe that The answer is