Which of the following are homogeneous in nature? 
(i) ice 
(ii) wood 
(iii) soil 
(iv) air 
 

A heterogeneous mixture is a mixture where throughout the solution the composition is not uniform.

To determine which substances are homogeneous, we need to understand that a homogeneous substance has a uniform composition and appearance throughout. Here is an explanation for each option:

• Ice: Ice is a homogeneous substance because it consists of solid water molecules arranged uniformly.
• Wood: Wood is not homogeneous. It has a non-uniform structure with varying components like fibers, cells, and other organic materials.
• Soil: Soil is heterogeneous because it is a mixture of different particles such as sand, clay, organic matter, and rocks, which are not evenly distributed.
• Air: Air is homogeneous when it is clean and free of pollutants because the gases (like nitrogen, oxygen, and carbon dioxide) are evenly mixed.

Thus, among the options, ice and air are homogeneous in nature.