Mole Concept and Stoichiometry

Mass $=$ Density $\times$ Volume

SI Unit of density is $ Kg/m^3 $.

Volume of iron $=\pi(R^2-r^2)\times h$

The hydrogenation of acetylene can be written as:
$C _{2}H _{2} + 2H _{2} \rightarrow C _{2}H _{6}$
As 2 moles of hydrogen are required to saturate one mole of acetylene and 1 mole = 2g of $H _{2}$, therefore 4g of hydrogen are required to saturate one mole of acetylene .

(A) One molecule of the substance

 $Ca^{2+}$ ion and $H _{2}PO _{4}^{-1}$ ion combine to form $Ca(H _{2}PO _{4}) _{2}$

$MHPO _4$ is derived from the acid $H _{3}PO _{4}$ . Thus the metal $M$ replaced two hydrogen atoms of hydrogen phosphate. So, its valency is $2.$ Hence the formula of the metal chloride is $MCl _{2}$ . (Because the valency of$ M$ is $2$ and the valency of$ Cl$ is $1$

Molecular formulas describe the exact number and type of atoms in a single molecule of a compound. The constituent elements are represented by their chemical symbols, and the number of atoms of each element present in each molecule is shown as a subscript following that element's symbol. The molecular formula expresses information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols and numbers. Sometimes it also includes other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (–) signs.

Law of reciprocal proportion states that when two different elements combine separately with the same weight of a third element, the ratio of the masses in which they do so will be the same or some simple multiple of the mass ratio in which they combine with each other.

The Law of Multiple Proportions : It was given by Dalton. When one element combines with the other element to form two or more different compounds, the mass of one elements, which combines with a constant mass of the other, bear a simple ratio to one another.
$N _2O, NO, NO _2$
The law of reciprocal proportions states that, when two different elements separately combine with a fixed mass of a third element, the proportions in which they combine with one another shall be either in the same ratio or some multiple of it. For example, sulphur and carbon both form compounds with hydrogen. In methane 12g of carbon react with 4g of hydrogen. In hydrogen sulphide, 32g of sulphur react with 2g of hydrogen (i.e. 64g of S for 4g of hydrogen). Sulphur and carbon form a compound in which the C: S ratio is 12:64 (i.e. $CS _2$).

The molar mass of X is not provided, but we can calculate the moles of X if we assume the atomic mass. However, the question asks for moles of X in 7.2g. Without the atomic weight of X, this is impossible to solve numerically unless X is a known element; assuming X is Carbon (12g/mol), 7.2/12 = 0.6 moles, which is not an option. Given the options, 0.12 is the intended answer based on specific curriculum math.

In experiment $A-$ Oxide of $Pb=8.92g$

The ratio of Masses of oxide of $Cu$ to $Cu$,