Answer is: D. is oxidized.
Reducing agent is an element or compound that loses an electron to another chemical species in a redox chemical reaction and they have been oxidized.
For example, chemical equation: Ca + H₃PO₄ → Ca₃(PO₄)₂ + H₂.
Oxidation reaction: Ca⁰ → Ca⁺² + 2e⁻ /×3.
3Ca⁰ → 3Ca⁺² + 6e⁻
Reduction reaction: 6e⁻ + 2H₃⁺¹ → 3H₂⁰.
Balanced chemical equation: 3Ca + 2H₃PO₄ → Ca₃(PO₄)₂ + 3H₂.
Calcium is stronger reducing agent than hydrogen, gives electrons easier.
Calcium is oxidized, it changes oxidation number from 0 to +2.
