11 4
n + B ----> ___?___ + He
2
7 8
A. Li or B. Li
235 4
Pa ------> ___?___ + He
91 2
A.230 or B. 231
Ac Ac
To determine the answer to the first equation, we need to find the atomic numbers of the elements n and B.
Looking at the periodic table, we can find that the atomic number of n is 11, which corresponds to sodium (Na).
The atomic number of B is 4, which corresponds to beryllium (Be).
So the balanced equation becomes:
Na + Be ----> ___?___ + He
Now we need to determine which element, A or B, corresponds to the missing element in the balanced equation.
Looking at the periodic table, we can find that the atomic number of A is 7, which corresponds to lithium (Li).
The atomic number of B is 8, which corresponds to oxygen (O).
Therefore, the missing element in the balanced equation is lithium (Li).
So the answer is A. Li.
To determine the answer to the second equation, we need to find the difference in atomic numbers between the starting element (Pa) and the resulting element (Ac).
The atomic number of Pa is 91, and the atomic number of Ac is 89.
So the difference in atomic numbers is 91 - 89 = 2.
This means that the resulting element should have an atomic number of 2 less than Pa.
The only option that fits this criteria is B. 231.
Therefore, the answer is B. 231.