87A+2 , the difference between electrons and neutronsnumber is 13. What is the atomic number of A?

The atomic number of an element is equal to the number of protons in its nucleus. In a neutral atom, the number of protons is also equal to the number of electrons.

Given the atomic mass number (A) is 87, and the difference between the number of electrons and neutrons is 13, we can set up the following equations:

1. A = number of protons (p) + number of neutrons (n) = 87
2. The difference between the number of electrons (e) and neutrons (n) is 13, so e - n = 13

Since the atom is neutral, the number of protons is equal to the number of electrons, so we can substitute p for e in the second equation:

p - n = 13

Now we have a system of two equations:

p + n = 87 p - n = 13

We can solve this system by adding the two equations together:

2p = 100

Divide both sides by 2 to solve for p:

p = 50

So, the atomic number of A is 50.