To determine which compound contains both polar and non-polar bonds, we need to analyze the types of bonds present in each molecule.

Concept:

A polar bond forms between two atoms with a significant difference in electronegativity, leading to unequal sharing of electrons and a partial positive and partial negative charge on the atoms (e.g., O-H, N-H, C-O). A non-polar bond forms between two atoms with similar or identical electronegativity, leading to equal sharing of electrons (e.g., C-C, H-H, O-O).

Why (B) is correct:

Let's analyze the structure of ${\mathrm{H}}_2{\mathrm{O}}_2$ (hydrogen peroxide):

The structure of hydrogen peroxide is H-O-O-H.

• The O-O bond is between two identical oxygen atoms. Since their electronegativity difference is zero, the O-O bond is non-polar.
• The O-H bonds are between oxygen and hydrogen atoms. Oxygen is significantly more electronegative than hydrogen, so the O-H bonds are polar.

Therefore, ${\mathrm{H}}_2{\mathrm{O}}_2$ contains both polar (O-H) and non-polar (O-O) bonds.

Option Analysis:

• A) ${\mathrm{NH}}_4\mathrm{Cl}$: This is an ionic compound consisting of ${\mathrm{NH}}_4^{+}$ and ${\mathrm{Cl}}^{-}$ ions. Within the ammonium ion ${\mathrm{NH}}_4^{+}$, the N-H bonds are polar. There are no non-polar covalent bonds.
• C) $\mathrm{HCN}$: The structure is H-C$\equiv$N. The C-H bond is slightly polar (though often considered non-polar in organic chemistry contexts, it has a small dipole). The C$\equiv$N bond is highly polar due to the large electronegativity difference between carbon and nitrogen. There are no non-polar bonds in this molecule.
• D) ${\mathrm{CH}}_4$: The structure is methane, with four C-H bonds. Carbon and hydrogen have a small electronegativity difference, making the C-H bonds slightly polar. However, due to the symmetrical tetrahedral geometry, the overall molecule is non-polar. There are no non-polar bonds within the molecule itself.

Correct Answer: (B)