If Meselson and Stahl's experiment is continued for three generations in bacteria. The ratio of $15N/15N:15N/14N:14N/14N$ containing DNA in the third generation would be

The correct option is C $0:1:3$
Meselson and Stahl's experiment is based on the semi-conservative replication of the DNA. It means that when a parental DNA undergoes replication, each strand of the parental DNA serves as a template and the new daughter strand is synthesized on the template strand. Keeping the semi-conservative replication in view, and starting with DNA strands having $15N$ and thereafter $14N$, the ratio comes out to be $0:1:3$ as shown below. Hence, the correct answer is $0:1:3$.