Hydrated Salt Na2CO3.x H2O:

The hydrated salt Na2CO3.x H2O is a crystalline solid that contains water molecules in its structure. The value of x represents the number of water molecules present in the compound.

Loss in Mass on Heating:

When the hydrated salt Na2CO3.x H2O is heated, it loses water molecules and becomes anhydrous. The percentage loss in mass on heating is given as 63%.

Calculation of Value of x:

To calculate the value of x, we need to use the following formula:

Percentage loss in mass = (Mass of water lost / Initial mass of hydrated salt) x 100

Substituting the given values, we get:

63% = (Mass of water lost / Initial mass of hydrated salt) x 100

Mass of water lost / Initial mass of hydrated salt = 0.63

Let the initial mass of hydrated salt be M, and the mass of water lost be m.

Then, we can write:

M - m = Mass of anhydrous salt

Also, we know that the anhydrous salt is formed by removing x water molecules from the hydrated salt.

So, we can write:

Mass of anhydrous salt = Mass of Na2CO3 + (x x Mass of water molecule)

Substituting the values, we get:

M - m = Mass of Na2CO3 + (x x 18)

Dividing both sides by the molar mass of Na2CO3, we get:

(M - m) / 106 = (Mass of Na2CO3 / Molar mass of Na2CO3) + (18x / Molar mass of Na2CO3)

Simplifying the equation, we get:

(M - m) / 106 = (Mass of Na2CO3 / 106) + (18x / 286)

Substituting the values, we get:

(M - m) / 106 = (Mass of Na2CO3 / 106) + (0.063 x x)

Since the value of x represents the number of water molecules, it must be a whole number. Therefore, we can assume different values of x and calculate the corresponding values of (Mass of Na2CO3 / 106) + (0.063 x x). The value of x for which this expression is closest to (M - m) / 106 is the correct value of x.

Using this method, we get the closest value of x as 10, which is the correct answer.