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The science teacher said, 'Water freezed
at
zero degree cCelsius (Into indirect speech)

The science teacher said that water freezes at zero degree Celsius.

Is your question correct?

Coz the scientific fact comes always in present.

remember, the goal of an adjective clause is to add more information to a noun or a pronoun. as you can see from the examples above, you can add information by including a longer adjective clause or tighten up a sentence by turning the adjective clause into an adjective phrase.