Plasmid are most widely used in genetic engineering.

Plasmids are used much more because they can replicate independent of the chromosomal DNA. Plastid is a major double-membrane organelle found in the cells of plants and algae. Mitochondria and ribosome are organelles found in the cells.

Hence, the correct option is (B).

Anhydrous magnesium chloride is fused with NaC𝑙 and anhydrous calcium chloride. The mixture is electrolysed at 700^∘C in the presence of an inert gas in an electrolytic cell. Magnesium is discharged at cathode. The purpose of the addition of NaC𝑙  and CaC𝑙 to anhydrous MgC𝑙₂ is to lower to fusion temperature and make the fused mass a good conductor of electricity.

Hence, the correct option is (A).

According to mass-flow hypothesis, there is a mass flow of mineral ions into the root along with transpiration current. Actually, transpiration creates a suction pressure or transpiration pull, conveyed from leaf xylem to root hair, which causes absorption of water from the soil passively. A large amount of ions are also absorbed along with the absorption of water. When the rate of transpiration is high, absorption of water increases due to increased suction pressure and along with water, absorption of ions also increases.

Hence, the correct option is (D).

To begin transcribing a gene, RNA polymerase binds to the DNA of the gene at a region called the promoter. The DNA opens up in the promoter region so that RNA polymerase can begin transcription. Each gene (or, in bacteria, each group of genes transcribed together) has its own promoter.

Hence, the correct option is (B).

Pyramid of numbers is the number of organisms in a food chain can represent graphically in a pyramid. Each bar represents the number of individuals at each trophic level in the food chain. Hence pyramid of numbers represent the number of herbivores and the carnivores at their successive trophic levels.

Hence, the correct option is (D).

Transgenesis is the process of insertion of a foreign gene into the genome of selected organism to improve its quality. The first transgenic experiments in mammals were performed in mice. Most of the transgenic experiments are still carried out with mice and hence they exists in maximum number.

The mouse is a very suitable model for these studies because they provide much information about the genome, inbred strains with specific genetic and phenotypic characteristics are available, mice are easy to handle and have a short generation interval, as well as they, shares most metabolic pathways and physiological processes with the human species.

Hence, the correct option is (C).

Most acidic hydrogen is present in

as two strong electron-withdrawing groups CO are present around the active methyline group.