Does Strangeness Have to Be Conserved?

Strangeness conservation requires the total strangeness of a reaction or decay (summing the strangeness of all the particles) is the same before and after the interaction. Strangeness conservation is not absolute: It is conserved in strong interactions and electromagnetic interactions but not in weak interactions.

Is the strangeness always conserved?

Strangeness is conserved in all but the weak interaction (this is because the weak interaction involves one type of quark changing into another as we have seen).

Why strangeness is not conserved in weak interaction?

In our modern understanding, strangeness is conserved during the strong and the electromagnetic interactions, but not during the weak interactions. Consequently, the lightest particles containing a strange quark cannot decay by the strong interaction, and must instead decay via the much slower weak interaction.