Statement A : Host cells are kept in Ca²⁺ ions to make them competent in order to accept rDNA.

Statement B : Biolistics or gene gun method is used to introduce rDNA directly into plant cells.

Statement A is true. In molecular biology and genetic engineering, the term "competent" refers to the ability of host cells to take up and incorporate foreign DNA, such as recombinant DNA (rDNA). Calcium ions (Ca²⁺) are often used in a process called calcium chloride transformation to make bacterial cells competent. The presence of calcium ions can make the cell membranes more permeable to DNA, allowing them to accept and uptake the foreign DNA.

Statement B is also true. Biolistics, commonly known as the gene gun method, is a biotechnology technique used to introduce foreign DNA, including rDNA, directly into plant cells. It involves coating microprojectiles, typically small metal particles, with the desired DNA and then shooting or "bombarding" these particles into plant cells.