NIOS Class 12 Chemistry — Important Questions (Board Exams 2027)

The actual electronic configuration of Copper (Z = 29) is [Ar] 3d¹⁰ 4s¹ instead of the Aufbau-predicted [Ar] 3d⁹ 4s². Which statement BEST explains this anomaly?

For the element with atomic number Z = 24 (Chromium), how many unpaired electrons are present in its ground state electronic configuration?

In Rutherford's gold foil experiment, approximately 1 in 10,000 alpha particles was deflected back. What does this observation specifically tell us about the nucleus?

How does atomic size change as we move from left to right across a period in the periodic table?

Which of the following correctly compares the sizes of a sodium atom (Na) and its ion (Na⁺)?

The first ionisation enthalpy of oxygen (O) is lower than that of nitrogen (N), even though oxygen has a higher atomic number. What is the best explanation for this anomaly?

The resonance hybrid of ozone (O₃) has equal bond lengths of 128 pm. The O=O double bond length is 121 pm and O-O single bond length is 148 pm. What does this tell us about the bond order in O₃?

Which of the following molecules has ZERO dipole moment despite having polar bonds?

In ethyne (C₂H₂), each carbon atom undergoes sp hybridisation. How many sigma (σ) bonds and pi (π) bonds are present in one molecule of ethyne?