Covalent bonding

In graphite, each carbon atom forms three covalent bonds with neighboring carbon atoms in a planar layer. Its fourth valence electron is delocalized over the layer rather than fixed in one bond. These delocalized electrons can move and carry charge, so graphite conducts electricity, especially along its layers. Option A is correct; graphite is not an ionic crystal, and its conductivity does not depend on forming ions in water.

Graphite has a layered covalent structure. Strong covalent bonds hold carbon atoms within each sheet, but the forces between adjacent sheets are weak. When graphite is rubbed between surfaces, these sheets slide over one another and reduce friction. Thus option A correctly explains its lubricating action. Option B describes diamond more closely, while graphite is neither rapidly water-soluble nor an ionic liquid, so C and D are incorrect.

Carbon has four valence electrons and therefore commonly shows valency four. In methane, its formula is CH₄: one carbon atom shares one electron with each of four hydrogen atoms. These shared pairs form four C–H single covalent bonds, giving carbon a stable octet and each hydrogen a stable duplet. The alternatives describe other or incomplete bonding, so option A is correct.

The governing concept is dominance in Mendelian inheritance. In a heterozygous individual, a dominant allele can determine the observable phenotype while the recessive allele remains present in the genotype. The recessive trait is usually expressed when suitable recessive alleles occur together, such as in a homozygous condition. Therefore A is correct. It does not appear in every condition, is not automatically lost, and is not defined as an acquired trait.