Solution:

(a) curl f - meaningless; a curl can only be taken of a vector field

(b) grad f - vector field; a gradient results in a vector field

(c) div F - scalar field; a divergence results in a scalar field

(d) curl( grad f ) - vector field; the curl of a vector field results in a vector field

(e) grad F - meaningless; a gradient can only be taken of a scalar field

(f) grad( div F ) - vector field; the gradient of a scalar field is a vector field

(g) div( grad f ) - scalar field; the divergence of a vector field is a scalar field

(h) grad ( div f ) - meaningless; the divergence of a scalar field can not be taken

(i) curl ( curl F ) - vector field; the curl of a vector field is a vector field

(j) div( div F ) - meaningless; the divergence of a scalar field can not be taken

(k) ( grad f ) x ( div F ) - meaningless; a vector and scalar field cannon be crossed

(l) div( curl( grad f )) - scalar field; the divergence of a vector field is a scalar field