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
Explanation:
1. Elements are substances made of the same kind of atoms, unlike compounds that are combination for different kinds of atoms. The elements in the reaction therefore are;
Cl and O₃
2. Yes, the equation is balanced. There is the same number of each element on either side of the equation. One (1) CL and three (3) O atoms.
3. Ozone is reduced. Other the other hand, Cl is oxidized. Remember a reduction reaction may involve the loss of one or more oxygen atoms or the acceptance of electrons. This occurs for O₃ which is reduced to O₂.
4. The equation complies with the conservation of matter as in the first law of thermodynamics. The number of atoms for each element on the other side of the equation remains the same. This means no matter(which also translated to energy) has been created or destroyed in the process.