The answer is Rubidium (Rb)
Answer:
Incomplete precipitation of barium sulfate
Explanation:
The student has precipitated and digested the barium sulfate on his/her side. But on the addition of 
in the solution, the solution become cloudy. This happened because incomplete precipitation of barium sulfate by the student. When is added, there are still sulfate ions present in the solution with combines with and forms 
and the formation of this precipitate makes the solution cloudy.
Answer:
Option (D) is definitely the answer.
Explanation:
Before going further, it is important to know what buffers and pH represent, which are keywords to answering this question.
Buffers is a special solution that can withstand or resist changes due to pH levels which may be as a result of an introduction of acidic or basic components into the blood. In other words, they maintain the stability of pH level in the human blood.
pH blood levels on the other hand, can be grouped into three: acidity, neutrality and alkalinity. Using a pH scale, one can determine its current level. In the human blood the pH level is near neutral and needs to be on a level near 7.4 in order to avoid a high rise or a drastic fall even if acidic or basic components come in or departs the blood stream.
Therefore, if one of the buffers that contributes to pH stability in human blood is carbonic acid, which is as a result of a combination of carbon dioxide and water in the blood stream. On getting to the lungs it is converted to water and subsequently released as waste. Maintaining this stability will definitely be to decrease the concentration of carbonic acid and increase that of water instead.
