Ice and Vaseline. Those are two melting compounds. When melting ice it turns into water and when melting Vaseline it melts into a oily liquid form. You can also freeze both of them and you can melt them again.
An ionic compound is composed of ionic bonds that are formed by transfer of electrons from one atom to the other. The atom that loses electrons acquires a positive charge (cation) while that which gains electrons acquires a negative charge.
In the case of sodium chloride; Sodium Na has 1 electron in its outer orbital while Chlorine Cl has 7 electrons. Thus, Cl requires 1 electron to complete its octet. This electron is donated by Na.
Thus, NaCl is essentially, Na⁺Cl⁻
Ans D) Chlorine becomes an anion by gaining an electron from sodium