Punjab Board Class 11 Chemistry — Important Questions 2026

According to Avogadro's Law, 2 volumes of H₂ react with 1 volume of O₂ to give 2 volumes of water vapour. Which statement BEST explains why Dalton's original atomic theory FAILED to predict this result?

A student dissolves 4 g of NaOH in enough water to prepare 250 mL of solution. What is the molarity of this NaOH solution? (Molar mass of NaOH = 40 g/mol)

Which of the following statements about the Law of Multiple Proportions is CORRECTLY illustrated?

The average atomic mass of chlorine is 35.5 u. Chlorine has two isotopes: ³⁵Cl (mass = 34.97 u) and ³⁷Cl (mass = 36.97 u). What is the approximate percentage abundance of ³⁵Cl?

In Thomson's model of the atom, how are electrons arranged?

In Rutherford's alpha-particle scattering experiment, what was the observation that led him to propose the existence of a nucleus?

For the atom ⁸⁰₃₅Br, what is the number of neutrons present in the nucleus?

Atoms that have the same mass number but different atomic numbers are called:

Na₂O reacts with water to form NaOH (basic oxide), while Cl₂O₇ reacts with water to form HClO₄ (acidic oxide). Which of the following oxides would be expected to be AMPHOTERIC?

The first ionization enthalpy of Al (577 kJ/mol) is LOWER than that of Mg (738 kJ/mol), even though Al has a higher atomic number. The BEST explanation is:

Mendeleev left gaps in his Periodic Table for undiscovered elements and named one 'Eka-Silicon'. He predicted its density as 5.5 g/cm³. The element discovered later (Germanium) had a density of 5.36 g/cm³. This achievement demonstrates which key strength of Mendeleev's Periodic Table?

Which of the following correctly explains WHY atomic radius DECREASES across a period from left to right?