Answer:
Reduced species and oxidizing agent: sulfur in the form of sulfate.
Oxidized species and reducing agent: chromium in the form of chromous hydroxide.
Explanation:
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In this case, for the reaction:

We can see that the oxidation states of sulfur and chromium change from +6 to +4 and +3 to +6 respectively; in such a way, since the oxidized species is the same reducing agent because it undergoes an increase in the oxidation state, we infer that chromium is it as it goes from +3 to +6.
Moreover, since the reduced species is the same oxidizing agent because it undergoes a decrease in the oxidation state, we infer that sulfur is it as it goes from +6 to +4.
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A non-sandblasted rock could be rough or smooth depending on how it was formed.
A sandblasted rock should be much smoother, since the sand blasts away any rough edges. It will, however, be slightly smaller due to losing those edges.
If a salt has a pH less than 7, then it is an acid. All acids start with a H in there formula. The only compound that starts with an H from the listed options is HCOOK.
So the salt HCOOK has a pH<7
The correct answer is D) Ar