Platelets, also known as thrombocytes, are responsible for blood clotting. They are small cell fragments in the blood that play a crucial role in preventing excessive bleeding when a blood vessel is injured. When damage occurs, platelets gather at the site and form a plug. They also release chemicals that trigger a cascade of reactions, leading to the formation of fibrin, a protein that stabilizes the clot. Lymphocytes and monocytes are types of white blood cells involved in immunity, while red blood cells transport oxygen. Thus, platelets are the correct answer. Understanding blood components is essential for studying human biology and medical conditions like hemophilia.

Plants absorb nitrogen in usable forms like ammonia (NH3) or nitrates. Atmospheric nitrogen cannot be directly used without fixation.

The Paris Climate Conference (COP21) was held in 2015, leading to the Paris Agreement aimed at limiting global warming below 2°C.

Balochistan became a province in 1970 after administrative reforms. Thus correct is 1970.

Ethiopia experienced a severe famine during 1983–1985, which became one of the most well-known humanitarian crises of the 20th century. It was caused by a combination of drought, political instability, and poor agricultural policies. The famine led to widespread starvation and the deaths of hundreds of thousands of people. It also triggered global humanitarian efforts, including aid campaigns and awareness programs. This event highlighted the importance of food security, disaster management, and international cooperation in addressing crises. Other periods listed are incorrect for this major famine. Thus, 1983–1985 is the correct answer, representing a significant historical event in global humanitarian efforts.