Serial Monitor not responding with AT commands

I’ve gone through every possible suggestion in this forum.
But i’m unable to fix the problem.

I made the connections of arduino UNO and ESP8266 as suggested in this forum.
After that as i open my serial monitor which showed me an error in opening serial port /dev/ttyACM0
I fixed this error by permitting ACM0 port by chmod command (again from the forum)

But now my serial monitor (on sending AT command) neither shows any error nor respond OK.
Please look into the issue asap as my project submission dates are nearer.

shivani_04: I made the connections of arduino UNO and ESP8266 as suggested in this forum.

There are hundreds of threads about connecting an Uno to an ESP8266 on this forum. How the heck should we be expected to know which suggestion you followed? You need to provide precise details of how you have the two connected if you want any help.

shivani_04: But now my serial monitor (on sending AT command) neither shows any error nor respond OK.

What is the baud rate setting in the dropdown menu at the bottom right corner of the Serial Monitor window?

Have you ever uploaded a sketch to your ESP8266? If so, that will have erased the AT firmware.