E.coli divides in 20 minutes. If  N¹⁵N¹⁵ containing E.coli is cultured in N¹⁴ medium then after 20 minutes

If E. coli containing N¹⁵N¹⁵ DNA is cultured in an N¹⁴ medium, and E. coli divides every 20 minutes, after 20 minutes of growth in the N¹⁴ medium, the distribution of DNA molecules within the bacterial population would be as follows:

Generation 1 (20 minutes): After one generation of growth (20 minutes), all the DNA in the population would become ¹⁴N¹⁵N (Hybrid DNA).