Answer: Li - Basic, S - Acidic , Al - Amphoteric
As we move from left to right in the periodic table, acidic nature increases and down the group acidic nature decreases. As electronegativity increases across the period, more polar compounds are formed due to which acidic nature increases.
As Li belongs to the first group it is more basic in nature, S belongs to the 16th group it is acidic in nature.Aluminium oxides can react with both acids and bases to form salts so, it is amphoteric in nature Oxides of metals like Al, Ga, Be, Sn, Zn, Pb are amphoteric in nature.