Which of the following is the number of moles of solute that is dissolved in 1 liter of solution?
a. percent by mass
b. molarity
c. percent by volume

I believe the correct answer is option B. Molarity is the number of moles of solute that is dissolved in 1 liter of solution. It is another way of expressing concentration of a mixture especially for solutions. Percent by mass is grams solute per grams of solution. Percent by volume is liter solute per liter per solution.

Alpha particles have positive charge, beta particles have negative charge, and answer 4 just doesn’t make sense. thus, you are left with only one possible answer.