Hey there Ritwik,
I'm sorry that your Chromecast is having issues connecting to your Wi-Fi ! I know networking problems can be difficult, so I'd be happy to help. For now, I would recommend that you try the troubleshooting steps listed in this article.
Let me know if that works, or if you run into any more issues while troubleshooting. I look forward to your response, and if you have any other questions or concerns for me, please let me know!