To make sure no cracks are in the crucible and also to remove any moisture present in the crucible by the process of heating.
Answer:- A. 
is not the correct formula.
Explanations:- Charge for Ba is +2 and charge for O is -2, Here the charges are in equal and opposite so their ratio is 1:1 and hence the formula must be BaO and not .
Rest of the formulas are correct as charge for Ca is +2 and charge for N is -3 . On criss cross we get the formula 
.
Charge for K is +1 and charge for Cl is -1 and so KCl is correct.
Charge for Li is +1 and that for S is -2. On criss cross we get the formula 
.
The atmosphere is a mixture of gasses that surrounds a planet, moon, or other celestial body
Answer:
the atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope
Explanation:
Average atomic mass = f1M1 + f2M2 + … + fnMn where f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope. The average atomic mass of an element can be found on the periodic table, typically under the elemental symbol.
