why my bit coin txn is still processing for more than 24 hours? Can any one help me why this txn is pending for more than 24 hours?

https://blockchain.info/tx/df040a6a683f99cdbf5ba92410c143bad2a2b042288630a07dad6c59cbd9be5e
The fee you paid for the transaction is currently non competitive at 149.712 sat/B.  The transaction volume for legacy transactions on the Bitcoin network is at capacity which means people are paying much higher fees than usual.

Sites like https://bitcoinfees.earn.com/ can help you estimate a competitive fee.  Looking at their estimates for 141-150 S/B transactions it looks like 5x as many transactions have been processed in the last 24 hours than are currently waiting to be processed.

If your transaction is time sensitive, look into "Replace By Fee" to speed up your stuck transaction.  https://bitcoinmagazine.com/articles/what-to-do-if-your-bitcoin-transaction-gets-stuck-1481042383/