The Nisab level for paying zakah for gold is 85 grams and for silver it is is 595 grams. But If suppose one is having 600 grams of silver than he is above the nisab level of silver and zakat is compulsory on him but if he converts this 600gms of silver into gold then the new value of the gold after conversion will be less than the nisab level of gold.
How we deal the above situation since both the casses are contradictory?
Please clarify the above situation as I am really confused why this 85gms of gold is there in comparison with 595gms of silver for judging the nisab level as both the values are not the same??

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The matter is easy, all praise be to Allaah, and there is nothing to worry about. That is because the Shaaree’ah imposed Zakah on gold and silver because they were the available currency at that time, and one Dinar of gold used to cost 10 Dirhams of silver, and Zakah is obligatory on 20 Dinars of gold, and on 200 Dirhams of silver. The estimation of each Nisaab with the grams of nowadays is what you mentioned in the question.

However, when the price and value of silver decreased much in comparison to the value of gold, then it became obligatory on whoever has the Nisaab of silver to pay Zakah on it, because it is a Zakatable item. Nonetheless, it should not be said that if it is sold it will not get the Nisaab of gold, because both of them are Zakatable items. Then, when people started to deal with banknotes which are neither gold nor silver, but they contain the same reason for which Zakah on gold and silver was made obligatory, which is being currency, so the scholars paralleled the banknotes to gold and silver, and made the Nisaab the same as when the Nisaab is obligatory on one of them [gold and silver]. So, few scholars valued the banknotes to gold in all cases, but the majority of the scholars valued it to the least Nisaab from both [gold and silver]. So, when the banknotes reach a level by which one may buy a Nisaab of either items [of gold or silver], then it becomes obligatory on him to pay Zakah as this is a means of fulfilling the need of the poor and because in principle it is an obligation to pay Zakah on money; Allaah Says (what means): {Take, [O Muhammad], from their wealth a charity by which you purify them and cause them increase.}[Quran 9:103]

For more benefit, please refer to Fatwa 86321.

Allaah Knows best.