Correct statements from the following are:
A. Nitrogen in oxidation states from +1 to +4 disproportionates in acid medium.
B. Nitrogen has the ability to form d$$\pi$$ - p$$\pi$$ multiple bonds with itself and other elements with small size and high electronegativity.
C. N-N single bond is stronger than P-P single bond.
D. Nitrogen has highest density in its group due to small size.
E. The maximum covalency of nitrogen is four since it has only four valence orbitals for bonding.
Choose the correct answer from the options given below:

Detailed Breakdown of Each Statement

• A. Nitrogen in oxidation states from +1 to +4 disproportionates in acid medium.
  Status: Correct
  In an acidic solution, nitrogen compounds with intermediate oxidation states (from +1 to +4) are unstable and typically undergo disproportionation (simultaneously oxidizing and reducing). For example, nitrous acid (+3 oxidation state) disproportionates into nitric acid (+5) and nitric oxide (+2):$$3HNO_2→HNO_3+2NO+H_2O$$
• B. Nitrogen has the ability to form dπ-pπ multiple bonds with itself and other elements...
  Status: Incorrect
  Nitrogen belongs to the second period of the periodic table and does not possess $$d$$-orbitals. Therefore, it cannot form $$d\pi-p\pi$$ bonds. Instead, it readily forms $$p\pi-p\pi$$ multiple bonds with itself ($$N≡N$$) and other small, highly electronegative elements like Carbon and Oxygen.
• C. $$N-N$$ single bond is stronger than $$P-P$$ single bond.
  Status: Incorrect
  The $$N-N$$ single bond is actually weaker than the $$P-P$$ single bond. Because of nitrogen's exceptionally small atomic size, the non-bonding lone pairs of electrons on adjacent nitrogen atoms experience high inter-electronic repulsion, weakening the single bond strength.
• D. Nitrogen has highest density in its group due to small size.
  Status: Incorrect
  Density generally increases down the group in Group 15 because the increase in atomic mass outweighs the increase in atomic volume. Nitrogen is a gas at room temperature and has the lowest density in its group, whereas bismuth ($$Bi$$) has the highest.
• E. The maximum covalency of nitrogen is four since it has only four valence orbitals for bonding.
  Status: Correct
  Nitrogen has the valence shell electronic configuration $$2s^22p^3$$. With only one $$2s$$ and three $$2p$$ orbitals available (and no vacant $$d$$-orbitals to expand its octet), it can form a maximum of four covalent bonds (e.g., as seen in $$NH4^+$$).

Summary Table