Answer:
They had a negative charge
Explanation:
According to Arrhenius theory, acid is a substance that releases H⁺ ions when dissolved in water.
In order to apply this theory, the substance must be soluble in water.
H₂SO₄ is highly soluble in water. It undergoes following dissociation reaction when dissolved in water.

From the above equation, we can see that H₂SO₄ forms 2 H⁺ ions when dissolved in water. Therefore it behaves as an acid according to Arrhenius theory.
The mass number goes on top, and the atomic number goes on bottom.
Therefore, the answer is C:
40
K
19