$A$ change in the physical state can be brought about:

What is meant by the following?
$(i)$ Molar mass
$(ii)$ Valency

$(a)$ Write the chemical symbols of two elements:
$(i)$ which are formed from the first letter of the element's name.
$(ii)$ whose name has been taken from the names of the elements in Latin.
$(b)$ Define Avogadro's constant and molar mass. How are they related to one mole of an atom,molecule,or ion?

State the number of atoms present in each of the following chemical species:
$(a)$ $CO_{3}^{2-}$
$(b)$ $PO_{4}^{3-}$
$(c)$ $P_{2}O_{5}$
$(d)$ $CO$

$(a)$ State the law of conservation of mass.
$(b)$ What mass of silver nitrate will react with $5.85 \, g$ of sodium chloride to produce $14.35 \, g$ of silver chloride and $8.5 \, g$ of sodium nitrate,if the law of conservation of mass is true?

Calculate the number of atoms in $120 \, g$ of calcium and $120 \, g$ of iron. Which one has more number of atoms and what is the difference? (Given: atomic mass of calcium $= 40 \, u$ and iron $= 56 \, u$)