The average atomic mass of a sample of an element $X$ is $16.2 \, u$. What are the percentages of isotopes $_8^{16}X$ and $_8^{18}X$ in the sample (in $\%$)?

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?

In a sample of ethyl ethanoate $(CH_{3}COOC_{2}H_{5})$,the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

State reasons for the following statements:
$(i)$ Some elements possess fractional atomic mass.
$(ii)$ Isotopes of an element have similar chemical properties.
$(iii)$ Noble gases are inert.

Write the electronic configuration of any one pair of isotopes and isobars.

Which of the following statements are true for an element?
$(i)$ Atomic number $=$ number of protons $+$ number of electrons
$(ii)$ Mass number $=$ number of protons $+$ number of neutrons
$(iii)$ Atomic mass $=$ number of protons $=$ number of neutrons
$(iv)$ Atomic number $=$ number of protons $=$ number of electrons