Calculate the molecular weight of a substance. in which the solution of this substance in the water has a concentration of 7 percent by weight, has a freezing point
equal to -0.89 ° c, set kf value of water = 1.86 ° c / m

Answer : The molecular weight of a substance is 157.3 g/mol

Explanation :

As we are given that 7 % by weight that means 7 grams of solute present in 100 grams of solution.

Mass of solute = 7 g

Mass of solution = 100 g

Mass of solvent = 100 - 7 = 93 g

Formula used :  

where,

= change in freezing point

= temperature of pure water =

= temperature of solution =

= freezing point constant of water =

m = molality

Now put all the given values in this formula, we get

Therefore, the molecular weight of a substance is 157.3 g/mol

its first and third is your answer i did the qustion the fourth isnt right