Final answer:
The appropriate needle size for an intramuscular injection in the deltoid site of an adult is a 1 to 1.5 inch needle with a gauge of 22 to 25. The best choice out of the given options is the 25 gauge, 1 inch needle.
Step-by-step explanation:
The appropriate needle size for an intramuscular injection in the deltoid site of an adult is a 1 to 1.5 inch needle with a gauge of 22 to 25. Out of the given options, the best choice would be the 25 gauge, 1 inch needle. This size is suitable for delivering medication into the muscle without causing excessive pain or injury.