2019 · Q96
Which one of the following statements is not correct?
General KnowledgeChemistry
- AElements are defined by the number of protons they possess.
- BIsobars are atoms having the same atomic number but different mass number.
- CThe mass number of an atom is equal to the number of nucleons in its nucleus.
- DValency is the combining capacity of an atom.
Explanation
Isobars are atoms of different elements that have the same mass number but different atomic numbers — e.g., carbon-14 and nitrogen-14. ‘Same atomic number, different mass number’ describes isotopes, not isobars, so this statement is incorrect. The other three are all correct: elements are defined by proton (atomic) number, mass number counts nucleons, and valency is combining capacity. Hence statement B is the not-correct one.