Yet another chemistry question!?

The question this time is: " Identify the two bases out of sodium hydroxide, potium nitrate, sodium chloride, lithium carbonate, sodium phosphate, and bariu sulphate" I know that sodium hydroxide is an alkali (which I think means a base) but I dont know how to find out whether a substance is acidic or alkaline! can someone help me find the other answer and an explanation of how you got the answer would be helpful as I have my chemistry exam tommorow!!!! Please respond quickly!...thanks!