Answer:
The electron from the ground state to occupy a next energy level. In this case,we say that the electron is excited
First, you need to find:
One mole of

is equivalent to how many grams?
Well, for this you have to look up the periodic table. According to the periodic table:
The atomic mass of Calcium Ca = 40.078 g (See in group 2)
The atomic mass of <span>Chlorine Cl = 35.45 g (See in group 17)
</span>
As there are two atoms of Chlorine present in

, therefore, the atomic mass of

would be:
Atomic mass of

= Atomic mass of Ca + 2 * Atomic mass of Cl
Atomic mass of

= 40.078 + 2 * 35.45 = 110.978 g
Now,
110.978 g of

= 1 mole.
75.9 g of

=

= 0.6839 moles.
Hence,
The total number of moles in 75.9g of

= 0.6839 moles
According to <span>Avogadro's number,
1 mole = 1 * </span>

molecules
0.6839 moles = 0.6839 *

molecules =

molecules
Ans: Number of molecules in 75.9g of
=
molecules
-i
Answer : The freezing point of the solution is, 260.503 K
Solution : Given,
Mass of methanol (solute) = 215 g
Mass of water (solvent) = 1000 g = 1 kg (1 kg = 1000 g)
Freezing depression constant = 
Formula used :

where,
= freezing point of water = 
= freezing point of solution
= freezing point constant
= mass of solute
= mass of solvent
= molar mass of solute
Now put all the given values in the above formula, we get

By rearranging the terms, we get the freezing point of solution.

Therefore, the freezing point of the solution is, 260.503 K