What is the primary source of minerals in the soil? 

Parent rock

The correct answer is option 3. Parent rock.

The primary source of minerals in the soil is Parent rock

Here's why:

Parent rock: This refers to the bedrock or underlying geological material from which the soil is formed. Over time, this rock is broken down through weathering processes like physical weathering (freezing and thawing) and chemical weathering (dissolution by water) to form soil particles. These breakdown products include minerals that become part of the soil composition.

While plants and animals can contribute some minerals to the soil through decomposition, the initial source and vast majority of minerals in soil come from the parent rock.

The other options you mentioned are not the primary source:

Plants: While decaying plant matter can add some organic material and nutrients to the soil, it's not the main source of minerals.

Animals: Similar to plants, animal decomposition can contribute some nutrients, but the mineral content is primarily derived from the parent rock.