NIOS Class 12 Chemistry — Important Questions 2026

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 many radial (spherical) nodes are present in the 4p orbital?

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?

Which of the following sequences correctly shows the increasing order of first ionisation enthalpy?

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?

The MO electronic configuration of N₂ molecule is σ1s², σ*1s², σ2s², σ*2s², π2p²(x), π2p²(y), σ2p². What is the bond order of N₂ and why does N₂ show diamagnetic behaviour?