How will you find the valency of chlorine, sulphur and magnesium ?

Explanation

(i) Valency of chlorine. The atomic number of chlorine is 17. The chlorine atom has 17 electrons, so its electron configuration is `underset("2, 8, 7")("K L M")`. A chlorine atom has 7 electrons in its valence shell (M shell). A chlorine atom can accept 1 more electron to achieve the inert gas electron arrangement (of 8 valence electrons), so the valency of chlorine is 1
(ii) Valency of sulphur. The atomic number of sulphur is 16. The sulphur atom has 16 electrons, so its electron distribution is `underset("2, 8, 6")("K L M")`. A sulphur atom has 6 electrons in its valence shell (M shell). A sulphur atom can accept 2 more electrons to acheive the inert gas electron arrangement (of eight valence electrons), so the valency of sulphur is 2
(iii) Valency of magnesium. The atomic number of magnesium is 12. The magnesium atom has 12 electrons, so its electron configuration is `underset("2, 8, 2")("K L M")`. A magnesium atom has 2 electrons in its outermost shell (M shell). A magnesium atom can lose its 2 outermost electrons to achieve the inert gas electron configuration (of 8 valence electrons), so the valency of magnesium is 2.