Which of the following scientists made no contribution to the develop…

The correct answer is Option (4) → Meselson and Stahl.

The double helix model of DNA was proposed in 1953 by James Watson and Francis Crick. They built it on two earlier pieces of work: the X-ray diffraction data of Maurice Wilkins and Rosalind Franklin, and Erwin Chargaff’s finding on base ratios in DNA.

Option (1) Erwin Chargaff. — Contributed to the double helix model. Chargaff found that in double stranded DNA the ratios of adenine to thymine and of guanine to cytosine are constant and equal to one. This supported the idea of base pairing between the two strands.

Option (2) James Watson and Francis Crick. — Contributed to the double helix model. Watson and Crick proposed the model itself, with base pairing between the two polynucleotide chains as its main feature.

Option (3) Maurice Wilkins and Rosalind Franklin. — Contributed to the double helix model. Wilkins and Franklin produced the X-ray diffraction data on which the model was based.

Option (4) Meselson and Stahl. — No contribution to the double helix model. Meselson and Stahl did their experiment in 1958, after the model was proposed. Using ¹⁵N and ¹⁴N in E. coli, they proved that DNA replicates semiconservatively. Their work was on replication, not on the structure of DNA.

NCERT Extract:
Structure of Polynucleotide Chain – “… It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA. One of the hallmarks of their proposition was base pairing between the two strands of polynucleotide chains. However, this proposition was also based on the observation of Erwin Chargaff that for a double stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equals one.”
The Experimental Proof – “It is now proven that DNA replicates semiconservatively. It was shown first in Escherichia coli and subsequently in higher organisms, such as plants and human cells. Matthew Meselson and Franklin Stahl performed the following experiment in 1958: … (iii) Thus, the DNA that was extracted from the culture one generation after the transfer from ¹⁵N to ¹⁴N medium [that is after 20 minutes; E. coli divides in 20 minutes] had a hybrid or intermediate density.”