If an atom of an element has atomic number = 15 and, mass number = 31, find the number of protons, electrons, neutrons in its atoms.

give the number of neutrons in an atom of element .

An element has mass number = 35 and atomic number = 17 find

(i) The number of neutrons in the element,

(ii) The number of electrons in the outermost shell.

Why do isotopes of an element have different physical properties?

How are the following pairs of atoms related?

₈X¹⁶, ₈X¹⁷, ₁₈Y⁴⁰, ₂₀Z⁴⁰,