Is maize $C_3$ or $C_4$?

Hint: The plants in which oxaloacetic acid (OAA) is the first stable product after the fixation of carbon dioxide are called $C_4$ plants. OAA is the four carbon compounds and hence, the plants are so-called $C_4$ plants. The $C_4$ plants have a special type of anatomy in their leaves. It is called Kranz anatomy. On the other hand, in $C_3$ plants, Kranz anatomy is not present. The Calvin cycle occurs in $C_3$ plants. Phosphoglyceric acid is the first stable product formed in $C_3$ plants.

Complete answer:
The plants that grow in hot and dry environmental conditions use the $C_4$ pathway. The $C_4$ pathway is seen in grasses such as sugarcane, maize etc.
The leaves of $C_4$ plants shows the following anatomical features-
The vascular bundles of $C_4$ plants are surrounded by several layers of bundle sheath cells. The chloroplasts of the bundle sheath cells are very large. There are no intercellular spaces between the bundle sheath cells.
The mesophyll cells have chloroplasts that are smaller in size.
Two enzymes are involved in the $C_4$ pathway- RuBisCO and PEPCase enzyme. RuBisCO enzyme is present in bundle sheath cells while PEPCase enzyme is present in mesophyll cells.
The plants that grow in cool and wet environmental conditions use the Calvin cycle. The Calvin cycle is seen in rice, wheat etc. They are most commonly found in temperate areas. Dark reactions occur in mesophyll cells of leaves. About 95% of the plants undergo the $C_3$ pathway.
The $C_4$ pathway provides advantage to plants in the following ways-
$C_4$ plants are more tolerant to high temperature
They use water more efficiently than other plants
In $C_4$ plants, no photorespiration takes place which is a wasteful phenomenon.
High carbon dioxide fixation increases the productivity of these plants.
The maize has Kranz anatomy; hence it is a $C_4$ plant.



Note:
As the $C_4$ pathway was discovered by Davidson Hatch and Charles Roger Slack, it is also called the Hatch and Slack pathway. The $C_4$ pathway provides many advantages to the plant over $C_3$ plants. It increases the concentration of carbon dioxide in the cells in which sugars are formed. Hence, the productivity of $C_4$ plants is higher than $C_3$ plants.