I'm planning to buy an ultra-wide monitor. Can a Dell laptop connected on hdmi drive the lg ultra wide montitor? Please help me.
Yes. The question would be what that LG monitor is running as a native resolution. Depending on it you will not be able to have it use that native resolution.
In order to figure it out look at the specs of the display and afterwards check the specs of your laptop graphics card. Keep in mind that older HDMI standards will not be able to display 4k or only within certain limits (e. g. 30 Hz).