ICSE Class 11 Chemistry — Important Questions 2026

According to Avogadro's hypothesis, under identical conditions of temperature and pressure, equal volumes of all gases contain:

The empirical formula of a compound is CH₂O and its molecular mass is 180 g/mol. What is its molecular formula?

Which law states that 'matter can neither be created nor destroyed in a chemical reaction'?

How many molecules are present in 0.5 moles of water (H₂O)? (Avogadro's number = 6.022 × 10²³)

The energy of an electron in the nth orbit of hydrogen-like ion He⁺ is given by Eₙ = –(2.178 × 10⁻¹⁸ × Z²)/n² J. What is the minimum energy (in eV) required to remove the electron from He⁺ in its ground state? (1 eV = 1.6 × 10⁻¹⁹ J)

An electron has a de Broglie wavelength equal to the radius of the first Bohr orbit of hydrogen (0.529 Å). What is the velocity of this electron? (h = 6.626 × 10⁻³⁴ Js, mₑ = 9.108 × 10⁻³¹ kg)

Which of the following sets of quantum numbers is VALID for an electron in a 4f orbital?

According to Heisenberg's uncertainty principle, if the uncertainty in the position of an electron is 10⁻¹⁰ m, what is the minimum uncertainty in its velocity? (h = 6.626 × 10⁻³⁴ Js, m = 9.108 × 10⁻³¹ kg)

Electron gain enthalpy of fluorine (–328 kJ/mol) is LESS negative than that of chlorine (–349 kJ/mol), contrary to the expected periodic trend. Which explanation is most accurate?

Using Mendeleev's predictions, ekasilicon was predicted to have an oxide formula of MO₂ and a chloride of MCl₄. When the element was discovered as Germanium (Z=32), these predictions were confirmed. What is the IUPAC systematic name for the element with atomic number 115, as per IUPAC nomenclature r

Which of the following correctly explains why the ionic radius of Mg²⁺ (0.65 Å) is smaller than that of Na⁺ (0.95 Å), given that both ions are isoelectronic with 10 electrons?

An element has the following ionisation energies (in kJ/mol): IE₁ = 577, IE₂ = 1817, IE₃ = 2745, IE₄ = 11,578, IE₅ = 14,831. To which group of the periodic table does this element most likely belong?