Zeta Metroids are heavily armored and incredibly powerful. They can spit fireballs and charge at Samus with devastating force. Their weak point is often difficult to hit.
Strategy: Zeta Metroids require a combination of charged shots, missiles, and careful dodging. Their armor makes them resistant to frontal attacks. Try to get behind them or hit them during their attack animations when they expose their vulnerable areas. The Screw Attack, if you have it, can be very effective against them. Be prepared for a prolonged battle, and ensure you have plenty of energy and missiles.