Question

Isobars are:
A. The atoms of the same element having the same atomic number but different mass numbers.
B. The atoms of the same element having the different atomic numbers but same mass numbers.
C. Atoms of different elements with the same atomic number which have different mass numbers.
D. Atoms of different elements with different atomic numbers which have the same mass number.

Answer 1

Hint: Two elements are said to be isobars of one another if they have different sets of electrons and the same number of nucleons. The term nucleon is a collective term used for the combination of neutron and proton altogether inside the nucleus of an atom.

Complete step by step answer:
Isobars are atoms (nuclides) of different chemical elements with varying chemical reactivities that have the same number of nucleons. The nucleon is a collective term used for the proton and neutron in an atom of a particular element. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number. The mass number can be defined as the total mass of proton and neutron inside the nucleus at the centre of an atom of any element. The atomic number can be defined as the number of protons or electrons present in the atom of the element.

So, the correct answer is Option D .

Note:
An example of a series of isobars would be \[{}^{40}C{a_{20}}\] and \[{}^{40}A{r_{18}}\]. Here, while the nuclei of these elements contain 40 nucleons, they contain varying numbers of protons and neutrons. In the case of calcium, the number of protons and electrons at ground state are 20 each and the number of neutrons is equal to the difference of the mass number and atomic number which is also 20 in the case of calcium. But, in the case of an argon atom, the number of electrons and the number of protons are both equal to 18 and the number of neutrons are equal to 22 here. This means that although both the atoms have the same number of nucleons, yet the atomic number is different and hence, the chemical reactivity is also different.