Leopard 1 v Leopard 2 How do the tanks bound for Ukraine compare

Ukraine is to receive hundreds of tanks from Nato nations - including UK Challenger 2s - as part of their support for Kyiv's defence against Russian aggression. The German-made Leopard 2 tank, widely regarded as the best of its kind in the world, is being sent to Ukraine. Kyiv is also set to receive at least 100 veteran Leopard 1 tanks from Denmark, Germany and the Netherlands. But what is the difference between Leopard 1 and Leopard 2 tanks being sent to Ukraine?