Help again, whats the molecule's name?

propenoic acid

The principal functional group is carboxyl group (–COOH), and thus the suffix of the name is -oic acid.
The longest chain including the –COOH group and C=C double (-en(e)- bond consists of 3 carbon atoms (prop(a)-), and there is no ambiguity for the position of C=C double bond, the name is thus propenoic acid.
According to IUPAC nomenclature, numbering "may" (not "must") be omitted in case of no ambiguity, the name 2-propenoic acid (in US) or prop-2-enoic acid (in Brit) may also be accepted.

In IUPAC its propenoic acid (the 2 is redundant) but it is almost universally known as acrylic acid.

2-Methylpropenoic acid: $500/lb. Acrylic acid: $ 500/ton.