What metal substance explodes when it meets water?

Sodium, potassium, lithium, rubidium, cesium

Tell a joke by the way:

A group of China children and American children asked them to measure the volume of a piece of metallic sodium.

China children took out all kinds of measuring tools, scales and densitometers, and kept trying to directly measure the length, width and height, and calculated the mass and density, which took nearly 4 hours;

American children took out a measuring cylinder full of water and put the sodium block in it. The increased volume is the volume of sodium block! The audience failed for their wisdom!

Then they took out the metal blocks of potassium, lithium, rubidium and cesium, put them into the water one by one, and measured the volume! ! ! ! ! ! !

The world cheers for them! ! ! ! ! !

(Laughter)