Daily Practice Problems

📝 SolutionThe Law of Conservation of Mass (Lavoisier) states that the total mass of reactants equals the total mass of products in a chemical reaction — mass is neither created nor destroyed. This is why chemical equations must always be balanced.

📝 SolutionOxygen gas exists as a diatomic molecule, meaning two oxygen atoms are chemically bonded together, giving the formula O$_2$. O$_3$ is ozone (a different, triatomic form), and 'O' alone refers to a single atom, not the naturally occurring gas.

📝 SolutionValency represents the combining capacity of an element — how many bonds one atom can form, often based on how many electrons it needs to gain, lose, or share to achieve a stable configuration. It has nothing to do with atomic mass or neutron count directly.

📝 SolutionUsing the criss-cross method: Al (valency 3) and O (valency 2) swap as subscripts, giving Al$_2$O$_3$. This ensures the total positive charge (2 × 3 = 6) balances the total negative charge (3 × 2 = 6).

📝 SolutionAvogadro's number is $6.022 \times 10^{23}$, defining the number of atoms, molecules, or particles in exactly 1 mole of any substance. This constant is the bridge between the microscopic (atoms) and macroscopic (grams) worlds in chemistry.