Element M reacts with oxygen to form an oxide with the formula MO. When MO is dissolved in water, the resulting solution is basic. Element M could be .Element M reacts with oxygen to form an oxide with the formula MO. When MO is dissolved in water, the resulting solution is basic. Element M could be .

Calcium

Explanation:

Since the element reacts with oxygen to form an oxide with the formula MO, the charge on the element is +2.

Also, since the oxide MO when dissolved in water is basic, the metal is an alkali earth metal.

From the above conditions;

The metal is not arsenic because arsenic is a metalloid has the  following oxides As₂O₃ and As₃O₅ and are respectively amphoteric and acidic in nature

The metal is not germanium because is a metalloid and even though germanium oxide has the formula GeO₂, it is amphoteric.

The metal is not chlorine because chlorine is a non-metal

The metal is definitely calcium because calcium oxide has the formula CaO and calcium is an alkaline earth metal.

The metal is not selenium because selenium is anon-meal and its oxide has the formula Se0₂ and is acidic