Let us calculate the structure of the electric shells of the Al atom. It has an atomic number of 13, so it has 13 electrons. The first 2 go to the first hell. The next 8 need to go to the second shell and the last 3 ones would go to the outermost shell. The outer shell, that is the most important one for chemical reactions, has thus 3 electrons. An atom always tries to have a completed outer shell (with either 2 or 8 atoms). It is easier for a cell to have a charge of +3 than a charge of -5 (smaller absolute value) and thus the Aluminum atom will try to get rid of the 3 electrons. In this process, it loses negative charge thus it will become positively charged. Hence, the correct answer is that it will prefer to lose 3 electrons and become positively charged.
