In a digital camera of 1080p can i shoot video in 720p to save space ?

Most all cameras that can shoot in Full HD (1080p) also have the option of shooting in HD (720p) Just look in your cameras user manual to see how to do that

no too likely. all consumer HD cameras use super compression, so the size of the frame is very minor consideration when it comes to the storage space required. the actual consumption of memory is the data rate and that is in turn limited by the processing speed of the CPU in the camera. Some cameras allow for data rate adjustment (such as SP instead of LP) as part of the "quality" setting. So sometimes you can chose to reduce quality setting to get more space.

Yes, you should be able to. All cameras that record Full HD (1920x1080) movies would also give you the option of recording in lower resolutions of HD 1280x720 and VGA 640x480. Just go into your camera Menu to see the options...read your camera Manual if not sure how to change it. Another option is to buy a larger capacity memory card so that you can continue to record movies in the highest resolution.

yes ofcourse you can but u need a good class memory card with larger space if u wanna record more n more minutes (both with 720p and 1080p) generally every one prefers 720p to save space just like u