Someone help me please I suck at science

How does the image distance (di) of a convex lens compare with the image distance of a concave lens? a. the image distance of the convex lens is positive, and that of the concave lens is negative. b. both are negative for a virtual image. c. both are positive for a virtual image d. the image distance of the convex lens is negative, and that of the concave lens is positive.

Which form of cell division creates the sperm and egg, resulting in half of the chromosomes as the other cells?

How do you know how many valence electrons an atom has?