Explanation

• Tropical rain forests support exceptionally high biodiversity but face severe threats from deforestation, agricultural expansion, logging, and habitat destruction.
• Subtropical rain forests are also threatened by habitat loss, land conversion, and human activities.

Last verified on 27-10-2026

Explanation

• Cichlids are freshwater fish found in several lakes, including Lake Victoria in Africa, which is famous for its diverse cichlid species.
• Overfishing, waste pollution, and agricultural runoff can damage aquatic ecosystems and contribute to the decline or extinction of fish species.
• Agricultural runoff may carry fertilizers and pesticides into lakes, causing eutrophication, reducing oxygen levels, and harming aquatic life.

Last verified on 27-10-2026

Explanation

• Sergei Nawaschin discovered double fertilization in flowering plants (angiosperms) in 1898.
• In double fertilization, one male gamete fuses with the egg cell to form a diploid zygote (2n), while the other fuses with the two polar nuclei to form the triploid endosperm (3n) in typical angiosperms.
• The zygote develops into the embryo, while the endosperm provides nourishment to the developing embryo.

Last verified on 27-10-2026

Explanation

• The Stark effect is the splitting or shifting of spectral lines of atoms or molecules due to an external electric field.
• The Stark effect is named after German physicist Johannes Stark, who discovered it in 1913.

Additional information:

• The Zeeman effect is the splitting of spectral lines due to an external magnetic field.
• The Photoelectric effect occurs when light ejects electrons from a material.

Last verified on 27-10-2026

Explanation

• Methane (CH₄) has four C–H bonds arranged symmetrically in a tetrahedral shape.
• Each C–H bond has a small bond dipole, but the four bond dipoles cancel one another because of the molecule’s symmetrical geometry.
• Therefore, methane has a zero net dipole moment.

Last verified on 27-10-2026

Explanation

• Silicon has atomic number 14, with the electronic configuration 1s² 2s² 2p⁶ 3s² 3p².
• When two electrons are removed from silicon, they are removed from the 3p subshell, producing Si²⁺ with the configuration 1s² 2s² 2p⁶ 3s².
• The outermost occupied orbital is then the 3s orbital, which is spherical in shape.

Last verified on 27-10-2026

Explanation

• Aluminium chloride (AlCl₃) is trigonal planar in its monomeric form, with aluminium at the centre and three chlorine atoms around it.
• The central aluminium atom is described as sp²-hybridized, forming three sigma bonds arranged at approximately 120°.
• Aluminium chloride can also form a dimer, Al₂Cl₆, under certain conditions.
• In the dimer, bridging chlorine atoms change the bonding arrangement.

Last verified on 27-10-2026

Explanation

• The azimuthal quantum number (l) identifies the subshell: l=0 for s, l=1 for p, l=2 for d, and l=3 for f.
• The number of orbitals in a subshell is calculated using 2l+1.
• For l=2, the number of orbitals is 2(2)+1=5.
• These five d orbitals are degenerate in an isolated atom, meaning they have the same energy.

Last verified on 27-10-2026

Explanation

• Acetic acid (CH₃COOH) is a weak acid that partially ionizes in water, producing hydrogen ions (H⁺) and acetate ions (CH₃COO⁻).
• Hydrogen sulphide (H₂S) is also a weak acid.
• Its presence does not directly add a common ion to the acetic acid ionization equilibrium.

Last verified on 27-10-2026

Explanation

• The degree of ionization is the fraction of electrolyte molecules that form ions in solution.
• Increasing concentration generally decreases the degree of ionization of a weak electrolyte because the equilibrium shifts toward the undissociated form.
• Dilution generally increases the degree of ionization of weak electrolytes.
• The effect of temperature depends on whether ionization is endothermic or exothermic.

Last verified on 27-10-2026