The power of a lens is +2D.
a . What do you mean by this ?
b How is power related to its focal length ?

Explanation

a. Power P = + 2D `therefore 2 = (1)/(f_((m)) ) , " " therefore f_((m)) = (1)/(2) = 0.5 ` m
it means power of a lens is + 2 dioptres and the lens is convex lens.
b. Power = `(1)/("focal length (in metre)")`
`P = (1)/(f_((m))) `