The positively charged molecule you are describing appears to be a hydronium ion (H₃O⁺), which forms when a water molecule (H₂O) gains a hydrogen ion (H⁺).
Among the options you provided, the correct way this molecule could form is:
A water molecule gained a hydrogen ion from another water molecule.
This occurs through the following process: When one water molecule (H₂O) donates a hydrogen ion (H⁺), it results in the formation of a hydronium ion (H₃O⁺), while the water molecule left behind becomes a hydroxide ion (OH⁻). This process is part of the self-ionization of water.