What background information did Watson and Crick have made available for developing a model of $DNA$ ? What was their contribution ?

- Watson and Crick had the following information which helped them to develop a model of $DNA.$

$(i)$ Chargaffs' law suggesting $\mathrm{A}=\mathrm{T}$ and $\mathrm{C}=\mathrm{G}$.

$(ii)$ Wilkins and Rosalind Franklin's work on $DNA$ crystal's $X$-ray diffraction studies about $DNA's$ physical structure.

$(iii)$ Watson and crick proposed $(a)$ How com-plementary bases may pair $(b)$ Semi conservative replication and $(c)$ Mutation through tautomerism