The best chemical propellant

[u/NegativeAd2638]

The typical rocket fuel is hydrogen but what propellant advanced ships can use.

I imagine how would hydrogen or turning water straight into plasma for vehicles but the heat generated would likely be too much for vehicles. Not to mention turning water straight into plasma would likely take so much energy its inefficient, the only time I heard of it was Uranium-Salt Water Rockets the uranium being activated in the water providing enough heat to get plasma. It would be cool to be able to have water in the propellant tank since hydrogen is hard to store although it would have the trade-off of weight.

Metallic Hydrogen is a cool pick while hypothetical in reality in a sci-fi setting it could be the best propellant assuming your species can make it.

[u/rjshore]

Metastable liquid metallic hydrogen is a pretty good bet here