A s-block element \( \text{(M)} \) reacts with oxygen to form an oxide of the formula \( \text{MO}_2 \). The oxide is pale yellow in colour and paramagnetic. The element \( \text{(M)} \) is:
\( \text{Na} \)
\( \text{K} \)
\( \text{Mg} \)
\( \text{Ca} \)