Oxygen is transported to the body’s cells by Red Blood Cells (RBCs). RBCs contain a special iron-containing pigment called hemoglobin, which has the ability to bind oxygen in the lungs and release it in body tissues where it is needed for cellular respiration. This process ensures that all body cells receive the oxygen required to produce energy (ATP).

Other options (for context)

• White Blood Cells (WBCs): Defend the body against infections and diseases, but do not carry oxygen.
• Hormones: Chemical messengers that regulate body functions, not involved in oxygen transport.
• Enzymes: Biological catalysts that speed up chemical reactions, not oxygen carriers.

Explanation: The liver is the largest gland in the human body. It is located in the upper right part of the abdomen, just below the diaphragm. The liver performs multiple vital functions, including the secretion of bile (which helps in digestion of fats), detoxification of harmful substances, storage of glycogen (energy reserve), and the synthesis of proteins and cholesterol. It also plays a crucial role in regulating blood sugar levels and metabolism. The average adult human liver weighs about 1.2 to 1.5 kilograms.

The Exosphere is the uppermost layer of the Earth's atmosphere. It lies above the thermosphere and gradually merges into outer space. The exosphere extends roughly from 700 km to 10,000 km above the Earth's surface. In this layer, air is extremely thin, and gas molecules such as hydrogen and helium are sparse and can even escape into space.

Other options (for context)

• Stratosphere: Second layer from the Earth’s surface; contains the ozone layer.
• Mesosphere: Lies above the stratosphere; meteors burn up here.
• Ionosphere: A region within the thermosphere important for radio communication, not the outermost layer.

Explanation: The primary colours of light are Red, Green, and Blue (RGB). These are the fundamental colours that can be combined in different proportions to produce all other colours in the visible spectrum. Yellow is not a primary colour—it is a secondary colour formed by mixing red and green light. This principle of colour mixing is used in television, computer screens, and other digital displays that use RGB colour models.

Explanation: The disease AIDS (Acquired Immuno Deficiency Syndrome) is caused by the HIV (Human Immunodeficiency Virus). HIV attacks the body’s immune system, specifically the CD4 or T-helper cells, weakening the body’s ability to fight infections and diseases. It spreads through unprotected sexual contact, sharing of infected needles, transfusion of contaminated blood, or from an infected mother to her child during birth or breastfeeding. There is no permanent cure, but antiretroviral therapy (ART) helps control the virus and prolong life.