# A nuclide contains 30 positively-charged particles, and 40 neutrally-charged massive particles. What is the nuclide?

Given a neutral atom we have ""^70Zn.
If it is a neutral atom (and we must assume so), for every electron there must be a positively charged nuclear proton. Thus $Z , \text{ the atomic number = 30}$. And thus the element is zinc metal, $Z n$, because this is how zinc is identified.
The mass number is simply the sum of nuclear protons and neutrons: $30 + 40 = 70$. Now this is a fairly rare isotope of $Z n$, maybe less that 1% abundance. The most probable zinc isotope is ""^64Zn. How many (i) electrons, and (ii) neutrons, does this isotope have?