Answer
The Watson Crick model explains Chargaff's rules (A=T, C=G) by having those bases required to physically pair, with the phospodiester backbone to the outside, meaning that the same numbers of those bases must be found in the double helix. It also satisfies the physical dimensions observed using X-ray crystallography by having two antiparallel strands bound to one another.
Work Step by Step
To answer this question, make a list of the data from the text (x-ray data, Chargaff's rules), and then, for each point, note how the Watson-Crick model satisfies each.
