The correct answer is option 3, which states that the two main constituents of granite are silica and aluminum.

Granite is a common type of igneous rock that is composed of various minerals. Silica, also known as silicon dioxide (SiO2), is the most abundant mineral found in granite. It gives granite its characteristic hardness and durability.

Aluminum is another major constituent of granite. It is present in the form of aluminum silicate minerals, such as feldspar and mica. These minerals contribute to the overall composition and texture of granite.

Options 1, 2, and 4 are not correct because they mention other elements like iron, silver, and iron oxide, which are not the main constituents of granite. It is important to understand the correct composition of granite, as it helps in identifying and categorizing rocks in geological studies.