Option 1 suggests that ATP stands for Adenosine tetra-phosphate. However, this is incorrect since "tetra-" means four, which does not accurately represent ATP, which only contains three phosphate groups.

Option 2 suggests that ATP stands for Adenine tetra-phosphate. This option is also incorrect because ATP contains adenosine, not adenine. Adenine is one of the components of adenosine, but it is not the complete name.

Option 3 suggests that ATP stands for Adenosine tri-phosphate. This is the correct answer. ATP consists of adenosine and three phosphate groups, hence "tri-" representing three.

Option 4 is stated as "None of the options are correct." However, this is not applicable in this case as option 3 (Adenosine tri-phosphate) is indeed the correct full form of ATP.

In conclusion, the correct full form of ATP is Adenosine tri-phosphate, as stated in option 3.