The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shell, giving them the same electronic configuration as a noble gas. Let's examine each option to determine which molecules follow the octet rule.

Option A: $\mathrm{CO}_2, \mathrm{C}_2 \mathrm{H}_4, \mathrm{NO}$ and $\mathrm{HCl}$

1. $\mathrm{CO}_2$: Carbon dioxide follows the octet rule. Carbon forms double bonds with two oxygen atoms, allowing it to have 8 electrons in its valence shell.

2. $\mathrm{C}_2 \mathrm{H}_4$: Ethylene follows the octet rule. Each carbon forms a double bond with the other carbon and single bonds with two hydrogen atoms, resulting in 8 electrons in the valence shell of the carbons.

3. $\mathrm{NO}$: Nitric oxide does not follow the octet rule. It has an odd number of electrons, making it a free radical.

4. $\mathrm{HCl}$: Hydrogen chloride follows the octet rule. Chlorine has 8 electrons in its valence shell when bonded with hydrogen.

Thus, three molecules $\mathrm{CO}_2$, $\mathrm{C}_2 \mathrm{H}_4$, and $\mathrm{HCl}$ follow the octet rule here.

Option B: $\mathrm{NO}_2, \mathrm{O}_3, \mathrm{HCl}$ and $\mathrm{H}_2 \mathrm{SO}_4$

1. $\mathrm{NO}_2$: Nitrogen dioxide does not follow the octet rule. It has an odd number of electrons.

2. $\mathrm{O}_3$: Ozone follows the octet rule. It has a resonance structure that allows each oxygen atom to have 8 electrons in its valence shell.

3. $\mathrm{HCl}$: As mentioned, hydrogen chloride follows the octet rule.

4. $\mathrm{H}_2 \mathrm{SO}_4$: Sulfuric acid follows the octet rule. All atoms achieve stable configurations through bonding.

Thus, three molecules $\mathrm{O}_3$, $\mathrm{HCl}$, and $\mathrm{H}_2 \mathrm{SO}_4$ follow the octet rule in this option.

Option C: $\mathrm{BCl}_3, \mathrm{NO}, \mathrm{NO}_2$ and $\mathrm{H}_2 \mathrm{SO}_4$

1. $\mathrm{BCl}_3$: Boron trichloride does not follow the octet rule. Boron has only 6 electrons in its valence shell.

2. $\mathrm{NO}$: As mentioned, nitric oxide does not follow the octet rule.

3. $\mathrm{NO}_2$: As mentioned, nitrogen dioxide does not follow the octet rule.

4. $\mathrm{H}_2 \mathrm{SO}_4$: Sulfuric acid follows the octet rule.

Thus, only one molecule, $\mathrm{H}_2 \mathrm{SO}_4$, follows the octet rule in this option.

Option D: $\mathrm{CO}_2, \mathrm{BCl}_3, \mathrm{O}_3$ and $\mathrm{C}_2 \mathrm{H}_4$

1. $\mathrm{CO}_2$: As mentioned, carbon dioxide follows the octet rule.

2. $\mathrm{BCl}_3$: As mentioned, boron trichloride does not follow the octet rule.

3. $\mathrm{O}_3$: As mentioned, ozone follows the octet rule.

4. $\mathrm{C}_2 \mathrm{H}_4$: As mentioned, ethylene follows the octet rule.

Thus, three molecules $\mathrm{CO}_2$, $\mathrm{O}_3$, and $\mathrm{C}_2 \mathrm{H}_4$ follow the octet rule in this option.

Conclusion: The correct options are Option A and Option D, both having at least three molecules that follow the octet rule.