What atom or ion has 12 protons 10 electrons?

atoms are made of protons, electrons and neutrons

atomic number of element is the number of protons. Atomic number is characteristic for that element

therefore by knowing the number of protons we know the atomic number, therefore we can use the periodic table to identify what the element is

element with atomic number 12 is - Mg

Atoms of elements are neutral in their ground state with equal number of protons and neutrons

Mg has 12 protons and 12 electrons

once atoms lose or gain electrons they are called ions

here Mg has only 10 electrons which means it has lost 2 electrons. then the net charge of Mg becomes

12 positive charges + 10 negative charges = 2 positive

Mg has a net charge of 2 and since its positively charged its called a cation

the ion with 12 protons and 10 electrons is Mg²⁺