Question

Planet A is an inner planet with no moon and hardly any atmosphere. Planet B is an inner planet with no moon but with a dense atmosphere. Which pair of planets is being described?

Answer 1

Well assuming that its talking about OUR solar system. A planet can only have no atmosphere (considering its an inner planet) if only it had been burned away by the heat of the sun. Thus you would assume Mercury, 1st planet, short of orbit period thus hot planet, meaning no atmosphere. The 2nd planet is Venus which as described does indeed have a dense atmosphere.