Answer : Photosynthesis is an example of a chemical reaction.
Explanation :
Photosynthesis : It is a type of chemical process which takes place in the plant cell. In photosynthesis process, the light energy converted into the chemical energy.
As plant needs carbon dioxide, water and light. During the photosynthesis, carbon dioxide, water and sunlight react to gives glucose, oxygen and water as a product.
The balanced reaction of photosynthesis will be,

Hence, photosynthesis is an example of a chemical reaction.
Out of the following give choices;
a. All DNA strands
contained only the heavy nitrogen isotope.
b. Half of the DNA strands contained only the light nitrogen
isotope.
c. All DNA strands contained both heavy and light nitrogen
isotopes.
d. All DNA strands contained only the lighter nitrogen
isotope.
The answer is b. Meselson–Stahl experiment demonstrated the semi-conservative model of DNA replication.
When DNA is replicated, one strand of the new double
helix strand is the parent's strand while the other is the newly synthesized
one. This made the semiconservative model stand out over the other two, dispersive
and conservative models.
Oxygen and Carbon Dioxide are the two gases being exchanged in the alveoli. Carbon Dioxide diffuses blood into the air, and oxygen diffuses from the air in the alveoli into the blood.
The answer to your question is D
A karyotype is a picture in which the chromosomes of a cell
have been stained so that the banding patterns of the chromosomes appear. This
way it is possible to view abnormalities in the chromosomes. Disorders such as aneuploidy can be diagnosed by karyotype.
It can also help identify local abnormalities on chromosomes such as abnormalities
in chromosome length, and location of the
centromere.