Give the increasing order of melting points of the following compounds:
a. I. `NaF` , II. `NaCl` , III. `NaBr`, IV. `NaI`
b. I. `CaI_(2)` , II. `CaBr_(2)` , III. `CaCl_(2)` , IV. `CaF_(2)` , V. `BeCl_(2)`
d. I. `NaCl` , II. `MgCl_(2)` , III. `AlCl_(3)`
e. I. `C Cl_(4)` , II. `BCl_(3)` , III. `BeCl_(2)` , IV. `LiCl`

Explanation

a. `NaF lt NaCl lt Na Br lt NaI`
m.pt. `(.^(@)C) 988 lt 801 lt 755 lt 651`
`:. I lt II lt III lt IV`
[Size of anion increases, covalent character increases and m.pt. decreases]
b. `CaF_(2) lt CaCl_(2) lt CaBr_(2) lt CaI_(2) (IV lt III lt II lt I)`
m.pt. `(0^(@)C) 1392 lt 772 lt 730 lt 575`
Since cations is same the charges on the ions are also same. So, the size of anion increases (group 17 ions), covalent character increases and m.pt decreases.
c. `Ba Cl_(2) lt Sr Cl_(2) lt CaCl_(2) lt MgCl_(2) lt BeCl_(2) (I lt II lt III lt IV lt V)`
m.pt. `(0^(@)C) 960 lt 872 lt 772 lt 712 lt 405`
Since anion is same the charges on the ions are also same. So, the size of cation decreases (group 2 ions), covalent character of cation decreases and m.pt. increases.
d. `overset(+1)(NaCl) lt overset(+2) (Mg) Cl_(2) lt overset(+3)(Al) Cl_(3)(I lt II lt III)`
The charge on the cation increases, covalent character increases and m.pt. decreases.
e. `overset(+1)(LiCl) lt overset(+2)(Be)Cl_(2) lt overset(+3)(BCl_(3)) lt overset(+4)(C Cl_(4)) (IV lt III lt II lt I)`
The charge on the cation increases, covalent character increases and m.pt. decreases.