Which element undergoes oxidation?HNO3 + H2S → NO + S + H2O

In the given reaction, HNO3 + H2S → NO + S + H2O, the element that undergoes oxidation is Sulfur (S).

Here's the step-by-step explanation:

1. Identify the oxidation states of each element in the reactants and products.

   In HNO3, the oxidation state of Nitrogen (N) is +5, Hydrogen (H) is +1, and Oxygen (O) is -2.

   In H2S, the oxidation state of Sulfur (S) is -2 and Hydrogen (H) is +1.

   In the products, the oxidation state of Nitrogen (N) in NO is +2, Oxygen (O) is -2, Sulfur (S) is 0 in S, and in H2O, Hydrogen (H) is +1 and Oxygen (O) is -2.

2. Compare the oxidation states from the reactants to the products.

   The oxidation state of Nitrogen (N) decreases from +5 in HNO3 to +2 in NO, which means it is reduced.

   The oxidation state of Sulfur (S) increases from -2 in H2S to 0 in S, which means it is oxidized.

Therefore, in the given reaction, Sulfur (S) undergoes oxidation.