Final answer:
A lower astronomical magnitude indicates a brighter object; thus, with Uranus at 6mg (mag) and Neptune at 8mg (mag), b)Neptune is fainter.
Step-by-step explanation:
The question seems to be referring to the apparent magnitudes of Uranus and Neptune, given in 'mg', which likely should be 'mag' for magnitudes. In astronomy, a lower magnitude means a brighter object, so if Uranus is 6mg (mag) and Neptune is 8mg (mag), then Uranus is brighter and Neptune is fainter. Therefore, the correct answer to the question is B) Neptune is fainter.
Neptune and Uranus are both ice giants with similar mass, but they have different atmospheric conditions and levels of internal heat. Despite Neptune having a small internal energy source and appearing bluer due to methane in its atmosphere, it does not emit as much measurable internal heat as Uranus. Neptune is also farther from the Sun, located at 30 AU (Astronomical Units) compared to Uranus at 19 AU.