Answer:
<em>B. Methyl yellow, which changes from yellow to red around a pH of
</em>
<em>4.0</em>
Explanation:
A pH indicator is a technique by which the pH of a solution can be known. The scenario in the question describes that the scientist wants to determine a pH after it gets converted from 6 to below 4. For this recognition, the scientist should use a methyl yellow indicator which will change from yellow to red once a pH around 4 is achieved.
Here something that might help
<span>
Most scientists believe that for half of </span>Earth's<span> 4.6-billion-year history, the</span>atmosphere<span> contained almost no </span>oxygen<span>. Cyanobacteria or blue-green algae became the first microbes to produce </span>oxygen<span> by photosynthesis, perhaps as long ago as 3.5 billion years ago and certainly by 2.7 billion years ago.</span>
Systemic circuit is defined as one of the two circuit of circulation that occurs in human body.
<h3><u>Explanation</u>:</h3>
The circulatory system is divided into two phases in the human body. They are:
A. Pulmonary circulation
B. Systemic circulation.
The pulmonary circulation is the short circuit of circulation that starts from the right ventricle, goes to lungs via pulmonary artery and returns to left auricle via pulmonary vein.
The systemic circulation is the bigger circuit that starts from the left ventricle, goes to each and every organ of the body via aorta, and returns to the right auricle via venacava.
Both plant and animal development is seeded in the perspective that a cell divides itself to form a tissue and tissues grouped will become an organ and the organism itself. The cell hierarchial model is followed in the development in both of these diverse however seemingly similar organisms.
<u>Answer</u>: Natural selection.
<u>Explanation</u>:
- The concept of <em>natural selection</em> was given by <em>Charles Darwin.</em>
- According to this concept, in a given environment the organisms that possess <em>better adaptations</em> have<em> higher chances of survival</em> and, leave behind a <em>greater number of progenies</em>.
- When malaria outbreak occurs, the allele frequencies change and only the organisms that possess the alleles which help them to <em>survive</em> this outbreak due to resistance against malarial infection will be selected by nature and<em> hence, this is an example of natural selection.</em>
