HELP

[Debb01]

Can someone help me figure these problems out?

The molar mass of a gas with a density of 5.8 g/L at 25 degrees and 740 mm Hg is closest to:

10g/mol
20 g/mol
150 g/mol
190 g/mol
none of these

The name for the compound CH₃CH₂CH₂CH₂CHO is:

pentakenol
pentanal
pentanoic acid
pentanol
pentyl ether

series ranked in order from largest to smallest (becoming more positive) electron affinity?

Ar, Cl, S
Cl, S, P
S, P, Si
P, Si, Al
none of these