Question

Read the given observations for four elements ${}_{Z_1}^{A_1}P{,}_{Z_2}^{A_2}Q{,}_{Z_3}^{A_3}R$ and ${}_{Z_4}^{A_4}S$ carefully. Here Z represents atomic number and A represents mass number.
(i) Elements P and R shows similar chemical properties.
(ii) Elements Q and S belong to different groups.
(iii) For elements P and R, $Z_1=Z_3$ and $A_1\ne A_3$.
(iv) For elements Q and S, $Z_2\ne Z_4$ and $A_2=A_4$.
Which of the following statements is correct?

• A. P and R are isobars while Q and S are isotopes
• B. P and S are isobars while Q and R are isotopes
• C. P and Q are isotopes while R and S are isobar
• D. P and R are isotopes while Q and S are isobar

Answer 1

Answer: (D)

P and R are isotopes while Q and S are isobar

Isotopes : Given by Soddy
They are the atoms of a given element which have the same atomic number (Z) but different mass number (A) i.e. They have same Nuclear charge (Z) but different number of Neutrons (AZ).
Isobars : Given by Aston
They are the atoms of different element which have the same mass number (A) but different Atomic number (Z) i.e They have different number of Electron, Protons & Neutrons But sum of number of neutrons & Protons i.e. number of nucleons remains same.
so P and R are isotopes while Q and S are isobar.