Cation used in PCR is

All polymerases require divalent cations for their activity but some tend to function in buffers containing Mn2+ as well, although a little less efficiently.dNTPs and oligonucleotides bind to Mg2+ and therefore its concentration should exceed the molar concentration of phosphate groups that are contributed from both the dNTPs and primers.dNTPs bind in equimolar concentration with Mg2+.