Answer:
The electric force between them decreases
Explanation:
The force between two charged particle is given by :

Where
r is the distance between charges
If the distance between the charges is increased, the electric force gets decreased as there is an inverse relation between force and distance.
Hence, the correct option is (c) "The electric force between them decreases"
Answer:
c. CH4 < NH3 because the NH bond is more polar than the CH bond.
Explanation:
Actually, the electronegativity difference between carbon and hydrogen is just about 0.4. This meager difference in electronegativity corresponds to a nonpolar bond between the two atoms.
However, the electronegativity difference between nitrogen and hydrogen is about 0.9. This larger electronegativity difference corresponds to the existence of a polar covalent bond between the two atoms.
Hence the N-H bond is significantly polar unlike the C-H bond. This implies that CH4 molecules are only held together by weak dispersion forces while NH3 molecules are held together by stronger dipole-dipole interactions and hydrogen bonds.
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