Give reasons
Aluminium utensils should not be kept in water overnight.

Explanation

Aluminium reacts with water and dissolved oxygen to form a thin film of aluminium oxide `(Al_2O_3)`.
`2Al (s) + O_2(g)+ H_2O(l) to Al_2O_3(s) + H_2(g)uarr`
A very small amount of `Al_2O_3` may dissolve in water to give a solution sontaining a few ppm of `Al^(3+)` ions. Since `Al^(3+)` ions are toxic to health, drinking water should not be kept in aluminium vessel overnight.