Propyl magnesium bromide can (loosely) be thought of as Propyl(-) and MgBr(+)
It is therefore a strong nucleophile (Pr-) and a very strong base. Think of how stable propane is, so how much it wants that proton back! In other words, how difficult is it to deprotonate propane? Very! pKa about 30ish! So it's vey basic.
So if you put propyl magnesium bromide in a proton rich environment (An alcohol, a carboxylic acid, water...) what will happen?