Carbon is able to form stable compounds because of:

Correct option is A

The correct answer is (A) its smaller atomic size.

The small atomic size of carbon contributes significantly to the stability of its compounds. Here's how:

1. Effective Bond Formation:
• Carbon's small size allows its nucleus to attract bonding electrons more effectively, leading to strong covalent bonds.
2. High Bond Strength:
• The strong bonds between carbon atoms and between carbon and other elements like hydrogen, oxygen, etc., result in stable compounds.
3. Versatile Bonding:
• The small atomic size also facilitates multiple bonding (single, double, and triple bonds) and complex molecular structures, enhancing the stability and diversity of carbon compounds.

Clarifications for Other Options:

• its allotropic forms: Allotropes like diamond and graphite result from carbon's versatility but are not directly responsible for the stability of carbon compounds.
• its ability to form covalent bond: While this is true, the smaller atomic size is the primary factor enabling strong covalent bonding.
• the presence of p-orbital: This aids bonding but is not the main reason for stability.