(a) In the formation of compound between two atoms A and B, A loses two electrons and B gains one electron.
(i) What is the nature of bond between A and B?
(ii) Suggest the formula of the compound formed between A and B.
(b) On similar lines explain the formation of `MgCl_(2)` molecule.
(c ) Common salt conducts electricity only in the molten state. Why?
(d) Why is melting point of NaCl high ?

Explanation

(a) `A overset(-2e^(-))(to) A ^(2+)`
`B overset (+1e^(-))(to)B^(-)`
(i) ionic bond is formed between A and B.

(b) (i) Mg has 2 electrons in its outermost shell so it loses its 2 electrons to achieve the insert gas configuration of eight valence electrons and forms positively chrged ion or divalent cation.
`underset("2 8 2")underset ("K L M")underset ("Magnesium atom")(Mg) overset(-2e^(-))(to) underset("2 8") underset("K L") underset("Magnesium ion")(Mg^(2+))`
(ii) Cl has 7 electrons in its outermost shell so it gains one electron to achieve the stable insert gas configuration and forms negatively charged ion or monovalent anion.
`underset("2 8 7")underset ("K L M")underset ("Chlorine atom")(Cl) overset(+e^(-))(to) underset("2 8 8") underset("K L M") underset("Chloride ion")(Cl^(-))`
`Mg^(2+)+2Cl^(-) to MgCl_(2)`
(c ) Common salt (NaCl) is an ionic compound which conducts electricity only in molten state because in molten state the electrostatic forces of attraction between oppositely charged ions `(Na^(+) and Cl^(-))` are overcome due to heat. Thus the ions move freely and conduct electricity.
(d) NaCl is an ionic compound so there is a strong force of attraction between the positively charged sodium ion and negatively charged chloride ion. Therefore a considerabel amount of energy is required to break the strong interionic attraction. Thus NaCl has high melting point.