Each element is defined by the number of

The atomic number of an element is equal to the number of protons in each atom and defines the element. For example, all carbon atoms contain 6 protons in their atomic nucleus; so the atomic number of carbon is 6.

What does the number of an element represent?

The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus.

First let's find how much 30Si in nature: 100%-92.2%-4.67%=3.13%

Average M = M(28Si) * 0.922 + M(29Si) * 0.0467 + M(30Si) * 0.0313;

Let's substitute all the values we know:

28.09 = 27.98*0.922 + 28.98*0.0467 +x * 0.0313;

x = 30.03 g/mol