Explanation

• Chromium (Cr) has atomic number 24.
• Expected configuration is [Ar] 3d⁴ 4s², but it is not stable.
• One 4s electron shifts to 3d to achieve stability.
• Half-filled d-subshell (3d⁵) is more stable due to symmetry and exchange energy.
• So chromium shows an exception in electronic configuration.

Last verified on 19-05-2026

Explanation

• Ionization energy is the energy needed to remove an electron from an atom.
• Beryllium (Be) has configuration: 1s² 2s² (stable 2s subshell).
• Boron (B) has configuration: 1s² 2s² 2p¹.
• The electron in boron is removed from a higher energy 2p orbital.
• 2p electron is farther and less tightly held than 2s, so easier to remove.

Last verified on 19-05-2026

Explanation

• Oxygen (O₂) shows a special magnetic behavior.
• It is attracted by a magnetic field (paramagnetic).
• This property comes from its electronic configuration.
• O₂ has two unpaired electrons in antibonding π orbitals*.
• Unpaired electrons create magnetic moment.

Last verified on 19-05-2026

Explanation

• Lattice energy depends on the attraction between ions in an ionic solid.
• It increases with higher ionic charge and smaller ionic size.
• More charge and smaller ions → stronger electrostatic force.
• Among given options, MgO has Mg²⁺ and O²⁻ ions.
• This gives it the strongest attraction and highest lattice energy.

Last verified on 19-05-2026

Explanation

• SF₄ (Sulfur tetrafluoride) is a molecule of sulfur and fluorine.
• According to VSEPR theory, its shape depends on electron pairs around sulfur.
• Sulfur has 4 bonding pairs + 1 lone pair = 5 electron domains.
• This arrangement gives a see-saw molecular shape.
• Lone pair causes distortion from perfect symmetry.

Last verified on 19-05-2026

Explanation

Each CN⁻ has −1 charge, so 6 CN⁻ = −6

Overall charge is −4, so Fe = +2

Last verified on 19-05-2026

Explanation

• A Daniell cell is a galvanic cell used to produce electricity.
• It has two electrodes: zinc (anode) and copper (cathode).
• Oxidation occurs at anode (Zn loses electrons).
• Reduction occurs at cathode (Cu gains electrons).
• So electrons always flow from anode to cathode.

Last verified on 19-05-2026

Explanation

• First law of Faraday: mass (m) ∝ charge (Q), and Q = It.
• • m = (Z × I × t) / 96500, where Z is electrochemical equivalent.

Last verified on 19-05-2026

Explanation

• Dehydration means removal of water (H₂O) from an alcohol.
• Concentrated acid (like H₂SO₄) acts as a dehydrating agent.
• Tertiary alcohols easily form stable carbocations.
• Elimination leads to formation of an alkene.
• Tertiary butanol gives a substituted alkene as product.

Last verified on 19-05-2026

Explanation

• HBr reacts with alkanes/alkenes depending on conditions.
• In typical exam context, propane undergoes substitution (free radical reaction).
• Bromine replaces hydrogen at different positions.
• Secondary carbon is more stable than primary carbon.
• So major product follows stability rule.

Last verified on 19-05-2026