What are the taxation with Bonds/T-bills?

T-Bills: T-Bills are for less than one year and part of buy in discount and sell at a premium, so you need to pay short-term capital gain (STCG) on this as per applicable slab rate.

Bonds: Interest income is credited to your bank account every 6 months, so it is considered as income from other source so tax need to pay as per your tax slab.

In case of any appreciation in the bond price, it is considered a capital gain. Long-term (LTCG) is 20% with indexation. If G-Sec are held for more than 3 years, it's come under LTCG, if less than 3 year then it's STCG.