Which property of an element can be used for its identification?

Find out the mass number of oxygen and sulphur atoms.

Which of the following species is electrically neutral and why?
$K^{+}, Cl^{-}, S^{2-}, P^{3-}, K$

What are isobars? Give one example.

Give a reason to explain why
$(a)$ isotopes of an element show identical chemical properties?
$(b)$ the atomic masses of elements are in fractions?
$(c)$ atoms combine with other atoms?

The average atomic mass of a sample of an element $y$ is $35.5 \,u$. What are the percentages of isotopes $_{17}^{37}y$ and $_{17}^{35}y$ in the sample?