Question

The boiling point of water at 735 mmHg is 99.07C. What percent by mass of NaCl should be present in a water soln to raise the boiling point to 100.0C? [Kb for water is 0.512 C kg solvent (mol solute )-1]

Answer 1

This is what you need to do.
First, use delta T = i*Kb*m and solve for m. i = 2 for NaCl and you have the other numbers in the problem.
Convert molality to percent by mass. Post your work if you get stuck.