Which experimental methods could be used to observe the progress of the following reaction?

Cr₂O₇^2-(aq) + 6I^-(aq) + 14H⁺(aq) → 2Cr³⁺(aq) + 3I₂(aq) + 7H₂O(l) 

I. Change in colour 
II. Change in mass 
III. Change in electrical conductivity 

A.  I and II only 

B.  I and III only 

C.  II and III only 

D.  I, II and III

Which is a correct statement for the reaction below? 

2MnO₄^-(aq) + 6H⁺(aq) + 5NO₂^-(aq) → 2Mn²⁺(aq) + 5NO₃^-(aq) + 3H₂O(l) 

A. MnO₄^- is the reducing agent and the oxidation number of Mn increases.
B. MnO₄^- is the oxidizing agent and the oxidation number of Mn decreases. 
C. NO₂^- is the reducing agent and the oxidation number of N decreases. 
D. NO₂^- is the oxidizing agent and the oxidation number of N increases.

What are the oxidation states of oxygen?

A voltaic cell is constructed from zinc and copper half-cells. Zinc is more reactive than copper. Which statement is correct when this cell produces electricity?

A. Electrons flow from the copper half-cell to the zinc half-cell. 

B. The concentration of Cu²⁺ (aq) increases. 

C. Electrons flow through the salt bridge. 

D. Negative ions flow through the salt bridge from the copper half-cell to the zinc half-cell.

Iron is a stronger reducing agent than silver.

What is correct when this voltaic cell is in operation?

What is correct in an electrolytic cell?