If you start with ten grams of sodium hydroxide, how many moles of sodium chloride will be produced?

Start by converting the mass of sodium hydroxide to moles, as this will allow you to use the #1:1# mole ratio that exists between the two reactants to determine how many moles of sodium chloride are produced.

#10 color(red)(cancel(color(black)("g"))) * "1 mole NaOH"/(40.0 color(red)(cancel(color(black)("g")))) = "0.25 moles NaOH"#

Now, the chemical reaction tells you that #1# mole of sodium hydroxide reacts with #1# mole of hydrochloric acid to produce #1# mole of aqueous sodium chloride.

Since the problem doesn't mention the quantity of hydrochloric acid that is available, you can assume that hydrochloric acid is in excess, which implies that all the moles of sodium hydroxide will be consumed.

This means that the reaction will produce

#0.25 color(red)(cancel(color(black)("moles NaOH"))) * "1 mole NaCl"/(1color(red)(cancel(color(black)("moles NaOH")))) = "0.25 moles NaCl"#

Assuming that the mass of sodium hydroxide was given as #"10 g"#, you must round the answer to one significant figure, so

#"no. of moles NaCl " = " 0.3 moles"#