Which of the following best describes the main difference between CH_4 and NH_3?

• A. CH_4 is a polar molecule, while NH_3 is nonpolar.
• B. CH_4 contains a double bond, whereas NH_3 contains only single bonds.
• C. CH_4 has four hydrogen atoms bonded to carbon, while NH_3 has three hydrogen atoms bonded to nitrogen and a lone pair of electrons.
• D. CH_4 and NH_3 have the same molecular geometry.

Answer: (C)

Verified step by step guidance

1. Identify the molecular formulas and structures of CH_4 (methane) and NH_3 (ammonia). CH_4 consists of one carbon atom bonded to four hydrogen atoms, while NH_3 consists of one nitrogen atom bonded to three hydrogen atoms and has one lone pair of electrons on nitrogen.
2. Recall that the presence of lone pairs affects molecular geometry and polarity. CH_4 has no lone pairs on the central atom, leading to a symmetrical tetrahedral shape, whereas NH_3 has one lone pair, which distorts its shape to a trigonal pyramidal geometry.
3. Understand that CH_4 is nonpolar because its symmetrical tetrahedral shape causes the dipole moments of the C-H bonds to cancel out. NH_3, however, is polar due to the lone pair creating an asymmetrical shape and a net dipole moment.
4. Evaluate the given options: the statement about polarity is reversed (CH_4 is nonpolar, NH_3 is polar), the statement about double bonds is incorrect (both have only single bonds), and the statement about molecular geometry is incorrect (they have different geometries).
5. Conclude that the best description is that CH_4 has four hydrogen atoms bonded to carbon with no lone pairs, while NH_3 has three hydrogen atoms bonded to nitrogen and one lone pair of electrons, which is the main difference affecting their properties.