Question

Zinc is put in concentrated sodium hydroxide what happens ?

Answer 1

Zinc react with sodium hydroxide and the zinc hydroxide is obtained.

Answer 2

This reaction would indeed be a single-replacement reaction as stated by Lorenzo, but Zinc would not replace sodium in this reaction because sodium is higher than zinc .
However, zinc can still replace another element in this reaction(Hydrogen). So replacing zinc with hydrogen produces sodium zincate and hydrogen gas:
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