If you have a 1/2 inch gap you don't want to use chaulk. You should buy 1/4 round or shoe mold for hardwood floors. Chaulk will look real bad. Use 1/4 round or shoe.
1/2" is definitely too large a gap to caulk. Quarter round is a common trim for baseboard to floor gaps. Caulk between the top of the quarter round and baseboard for a nice finished look.
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