The atomic number and the mass number of certain elements are given below in the table. Element A B C D E F Atomic number 1 3 8 18 20 1 Mass number 2 7 16 40 40 1 Select a pair of isobar and isotope from the above table.

A 1 2 , B 3 7 , C 8 16 , D 18 40 , E 20 40 , F 1 1 Element A and F are isotopes. Elements both A and F have the same atomic number (1) but different mass numbers i.e. 2, and 1 respectively. So, it is an isotopic pair. Isotopes are chemical elements that have the same atomic number but different mass numbers. Element D and E are isobars. Elements D and E have the same mass number (40), but different atomic numbers i.e. 18 and 20 respectively. Isobars are those elements that have a different atomic number but the same mass number.

The atomic number and the mass number of certain elements are given below in the table. Element A B C D E F Atomic number 1 3 8 18 20 1 Mass number 2 7 16 40 40 1 What would be the valency of elements B and E .

The atomic number of B is 3 . Its electronic configuration is 2 , 1 . Thus, the valency of element B = 1 The atomic number of E is 20 . Its electronic configuration is 2 , 8 , 8 , 2 . The valency of element E = 2 , since it has two valence electrons.