The most appropriate size needle for administering an im injection for a 200-lb male with a non-viscous solution is:

The appropriate needle size would be 1.5 in, 22 gauge to ensure intramuscular injection into the deltoid muscle. The skin at the site for the injection should be spread tight by using the thumb and forefinger; this helps in isolating the muscle. When administering the needle, it should be fully inserted into the muscle at a 90° angle.