1. Could you open the window, please?<br/><br/> 2. He opened the window.<br/><br/><br/> 3. Now there is an open window. [This is correct.]<br/><br/> Is the second sentence fine?<br/><br/> The word 'open' is both an adjective and a verb. <br/><br/> So as a verb, the forms are 'open' , 'opened' and 'opening'.<br/><br/> You use an 'opener' to open canned food.<br/><br/> You will find an 'opening' in a water tank; If there is an opening, the water will leak.<br/>