<span>C. It is in the row below and therefore more reactive </span>
Metal usually donates electrons. The concept behind this phenomenon is stability. The elements with the most stable electronic configuration are the noble gases in Group 5A. As a result, the other elements donate or accept electrons so that they would be like the noble gases. Since metals are past their nearest noble gas element, they have to shed their electrons. When they do, they become cations which are positively charged ions.
The rate of the reaction is measurable quantity that refers to the amount or how much is are chemical substances reagents used up or converted into the product over some period of time.
Rate = change in the amount/time.
This can indirectly be observed through many ways, such as the volume of gas given off if the byproduct is a gas being produced, the colour of the solution etc.
The student is worng, because CO₂ is acidic oxide. When an acidic oxide reacts with water, acid is formed. In the student's case, the following reaction happens:
H₂O + CO₂ ⇒ H₂CO₃
The H₂CO₃ is carbonic acid and it is the scoure of the H⁺ atoms. The sample is not contaminated.