The most recive isotope of H is

Explanation

Matthew Meselson and Franklin Stahl, grow E. Coli in a medium containing `""^(15)NH_(4)Cl` and observed `15_(N)` was incorporated in newly synthesized DNA. This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride density gradient.
They transformed the cells into a medium with `""^(14)NH_(4)Cl` (normal) and took samples at various time intervals and extracted the DNA that remained as double stranded helices. The various samples were separated independently on cesium chloride (cscl) gradients to measure the densities of DNA. Thus the DNA that was extracted from the culture, one generation after the another generation (40 mts) was composed of equal amounts of this hybrid DNA and of .Light. DNA.