A sentence has been given in Direct/Indirect Speech. Out of the four given alternatives, select the one which best expresses the same sentence in Indirect/Direct Speech.
There are two elements-calcium (atomic number 20) and argon (atomic number 18). The mass number of both the elements is 40. They are therefore known as
Isotopes-These are atoms of the elements having the same atomic number but different mass number., Isobars-These are atoms of same mass number but different atomic number., Isotones-These are atoms of different elements having same number of neutrons.