The mass of one steel screw is $4.11 \, g$. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth $(5.98 \times 10^{24} \, kg)$. Which one of the two is heavier and by how many times?

$(a)$ Write the chemical formula of sodium sulphate.
$(b)$ Name one element each that forms a diatomic and a tetraatomic molecule.

Calculate the number of particles in each of the following:
$(a)$ $48 \,g$ of $Mg$
$(b)$ $8 \,g$ of $O_2$
$(c)$ $0.1$ mole of carbon (Atomic mass $Mg = 24 \,u, O = 16 \,u, C = 12 \,u$,Avogadro constant $= 6.022 \times 10^{23}$)

$A$ $0.24 \, g$ sample of a compound of oxygen and boron was found by analysis to contain $0.096 \, g$ of boron and $0.144 \, g$ of oxygen. Calculate the percentage composition of the compound by weight.

$(a)$ 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?

$(a)$ Calculate the mass of $0.5$ mole of oxygen atoms.
$(b)$ Calculate the number of molecules of glucose present in its $90 \ g$ (molecular mass of glucose is $180 \ u$). (Avogadro constant $= 6.022 \times 10^{23} \ mol^{-1}$)
$(c)$ Calculate the number of moles of water in $2 \ g$ of water.
(Atomic mass of $H = 1 \ u, O = 16 \ u$)