You may consider it under capital gain tax
I think while filling return you have to show it under income.grom other source.column. but not very sure about it.
Capital Gains tax and Income from other sources are two different heads. You can't show CG under Income from other sources.
How much tax applicable on Bitcoin? Any idea,
It really depends upon the way you earned Bitcoin. Say, you bought 1 BTC from INR 3 lakhs and now it worth 5 lakhs then 5 less 3 i.e. 2 lakhs will be your capital gain. So you have to pay CG tax on 2 lakhs. Such CG tax could be long-term if you bought 1 BTC more than 3 years ago and is chargeable at the rate of 20% or it could be short-term if bought within 3 years and chargeable at the rate of your income slab.
If you never bought BTC and simply earned it via campaigns and bounties, you have to show such income under PGBP or Income from other sources. Listing such income as contract income under Profit from Business or Profession (PGBP) is better option since you can claim deductions and lower your tax while you have to pay tax on full income if you include it under Other Sources.
Recently, ClearTax launched service which could help you determining tax on Crypto Income. You can refer it too.