Element X forms a chloride which is hydrolysed by water to form an acidic solution. Oxide of X reacts with an acid to form a salt. What is X?

The marking scheme gives answer B. Aluminium chloride hydrolyses to give an acidic solution. Aluminium oxide is amphoteric and reacts with acids to form salts. Silicon chloride also hydrolyses but $SiO_2$ does not react with acids.