Among the following compounds, the one with the least percentage of chlorine is

Vinyl chloride

The correct answer is option 2. Vinyl chloride.

% of chlorine \(= \frac{\text{Mass of chlorine}}{\text{Mass of the organic compound }} × 100\)

(1) Molecular mass of Chloroform \((CHCl_3)\) \(= 12 + 1 + 3 × 35.5 = 119.5\)

% of chlorine \(= \frac{106.5}{119.5} × 100 = 89.12\)%

(2) Molecular mass of Vinyl chloride \((C_2H_3Cl)\) \(= 2 × 12 + 3 ×1 + 35.5 = 62.5\)

% of chlorine \(= \frac{35.5}{62.5} × 100 = 56.8\)%

(3) Molecular mass of Gammaxene \((C_6H_6Cl_6)\) \(= 6 × 12 + 6 × 1 + 6 × 35.5 = 291\)

% of chlorine \(= \frac{213}{291} × 100 = 73.19\)%

(4) Molecular mass of Chloral \((C_2HOCl_3)\) \(= 2 × 12 +  1 + 16 + 3 × 35.5 = 147.5\)

% of chlorine \(= \frac{106.5}{147.5} × 100 = 72.2\)%

From the above calculations we can analyze that vinyl chloride has the lowest percentage of chlorine.

So, the correct answer is (2) Vinyl chloride.