Explanation

• Gibbs free energy (ΔG) determines spontaneity of a reaction.
• A reaction is spontaneous when it can proceed on its own.
• For spontaneity, energy must be released during the process.
• This means the system moves toward lower energy state.
• Therefore, ΔG must be less than zero.

Last verified on 19-05-2026

Explanation

• Gibbs free energy change depends on reaction quotient (Q).
• Relation: ΔG = ΔG° + RT ln Q.
• When Q increases, ln Q increases.
• This makes ΔG more positive.
• So the system becomes less spontaneous in forward direction.

Last verified on 19-05-2026

Explanation

• Effective nuclear charge (Zₑff) is the net positive charge felt by an electron.
• It increases when shielding is less and penetration is higher.
• For a given shell (n = 3), penetration order is: 3s > 3p > 3d.
• 3s electrons are closest to the nucleus and least shielded.
• Therefore, they experience the strongest attraction from the nucleus.

Last verified on 19-05-2026

Explanation

• SN2 is a bimolecular nucleophilic substitution reaction.
• It occurs in a single step with a backside attack by nucleophile.
• This causes inversion of configuration (Walden inversion).
• Rate depends on both substrate and nucleophile concentration.
• It is a second-order reaction.

Last verified on 19-05-2026

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