3- fully folded proteins typically have polar side chains on their surfaces, where electrostatic attractions and hydrogen bonds can form between the polar group on the amino acid and the polar molecules in the solvent. in contrast, some proteins have a polar side chain in their hydrophobic interior. which of the following would not occur to accommodate an internal, polar side chain?
a) a hydrogen bond forms between two polar side chains. b) a hydrogen bond forms between a polar side chain and protein backbone. c) a hydrogen bond forms between a polar side chain and a hydrophobic side chain. d) hydrogen bonds form between polar side chains and a buried water molecule.

Option C= A hydrogen bond formed between a polar side chain and a hydrophobic side chain.

Explanation:

All three given options a, b and d have common mechanism to accommodate the polar amino acid.

A= A hydrogen bond forms between two polar side chains.

B= A hydrogen bond from between a polar side chain and protein back bone.

D =  hydrogen bond form between polar side chains and a buried water molecules.

All these are use to accommodate the polar amino acid.

While option C is not used. which is:

A hydrogen bond formed between a polar side chain and a hydrophobic side chain.

that's what i got you can count the number of atoms

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3