Mole = Mass / Molar mass
6.12 moles = Mass / 74.92 g/mol
Mass = 6.12 moles x 74.92 g/mol
Mass = 458.51g
Remember that a conjugate acid-base pair will differ only by one proton.
None of the options you listed are conjugate acid-base pairs as none of them differ only by one proton (or H⁺)
An example of a conjugate acid-base pair would be NH₃ and NH₄⁺NH₃ + H₂O --> NH₄⁺ + OH⁻NH3 is the base, and NH₄⁺ is the conjugate acid
Supercooling<span>, a state where liquids do not solidify even below their normal freezing point. Means sometimes we have liquid water below 0 degree C.</span>
Density is independent of amount while mass is dependent