1. Recall the octet rule
   A molecule is said to follow the octet rule if the central/main atoms attain 8 electrons in their valence shell after bonding.
   Common exceptions here are:

• Incomplete octet: e.g. $\mathrm{BCl_3}$
• Odd-electron molecules: e.g. $\mathrm{NO}, \mathrm{NO_2}$
• Expanded octet: e.g. $\mathrm{H_2SO_4}$ (sulfur can have more than 8 electrons)

We now check each species.

2. Check the molecules one by one

(i) $\mathrm{CO_2}$

Structure: $\mathrm{O=C=O}$
Carbon has 4 shared pairs around it $\Rightarrow 8$ electrons.
Each oxygen also has an octet.
$\Rightarrow$ Follows octet rule

(ii) $\mathrm{C_2H_4}$

Structure: $\mathrm{H_2C=CH_2}$
Each carbon forms 4 bonds total, so each carbon has 8 electrons around it.
Hydrogen follows duplet rule.
$\Rightarrow$ Follows octet rule

(iii) $\mathrm{NO}$

Total valence electrons $= 5+6=11$ (odd number)
Odd-electron molecule, so complete octet is not possible for all atoms.
$\Rightarrow$ Does not follow octet rule

(iv) $\mathrm{HCl}$

Chlorine has 3 lone pairs + 1 bond $\Rightarrow 8$ electrons around Cl.
Hydrogen has duplet.
$\Rightarrow$ Follows octet rule

(v) $\mathrm{NO_2}$

Total valence electrons $= 5+2\times 6 = 17$ (odd number)
Odd-electron molecule.
$\Rightarrow$ Does not follow octet rule

(vi) $\mathrm{O_3}$

Ozone has resonance structures such as: $\mathrm{O=O-O} \leftrightarrow \mathrm{O-O=O}$ In these structures, each oxygen can be represented with an octet.
$\Rightarrow$ Follows octet rule

(vii) $\mathrm{H_2SO_4}$

Usual Lewis structure has sulfur bonded to four oxygens, often shown with two $\mathrm{S=O}$ bonds and two $\mathrm{S-OH}$ bonds. Then sulfur has 12 electrons around it.
$\Rightarrow$ Expanded octet, so does not follow octet rule

(viii) $\mathrm{BCl_3}$

Boron forms 3 bonds only, so it has 6 electrons around it.
$\Rightarrow$ Incomplete octet, so does not follow octet rule

3. Evaluate each option

Option A: $\mathrm{CO_2, C_2H_4, NO, HCl}$

• $\mathrm{CO_2}$: follows
• $\mathrm{C_2H_4}$: follows
• $\mathrm{NO}$: does not follow
• $\mathrm{HCl}$: follows

So, 3 molecules follow octet rule.
$\Rightarrow$ A is correct

Option B: $\mathrm{NO_2, O_3, HCl, H_2SO_4}$

• $\mathrm{NO_2}$: does not follow
• $\mathrm{O_3}$: follows
• $\mathrm{HCl}$: follows
• $\mathrm{H_2SO_4}$: does not follow

So, only 2 molecules follow octet rule.
$\Rightarrow$ B is incorrect

Option C: $\mathrm{BCl_3, NO, NO_2, H_2SO_4}$

• $\mathrm{BCl_3}$: does not follow
• $\mathrm{NO}$: does not follow
• $\mathrm{NO_2}$: does not follow
• $\mathrm{H_2SO_4}$: does not follow

So, 0 molecules follow octet rule.
$\Rightarrow$ C is incorrect

Option D: $\mathrm{CO_2, BCl_3, O_3, C_2H_4}$

• $\mathrm{CO_2}$: follows
• $\mathrm{BCl_3}$: does not follow
• $\mathrm{O_3}$: follows
• $\mathrm{C_2H_4}$: follows

So, 3 molecules follow octet rule.
$\Rightarrow$ D is correct

4. Final answer The options in which at least three molecules follow octet rule are: $\boxed{A, D}$

5. Comparison with stored correct answer Stored correct answer: $A, D$
   Derived answer: $A, D$
   Hence, they agree.