The Paris Climate Conference, officially known as COP21, was held in 2015 in Paris, France. It brought together representatives from nearly every country to address the growing threat of climate change. The conference resulted in the historic Paris Agreement, a global pact aimed at limiting the rise in average global temperatures to well below 2°C above pre-industrial levels, with efforts to restrict it to 1.5°C. This agreement is significant because it marked the first time that both developed and developing nations committed to reducing greenhouse gas emissions. Countries pledged to set nationally determined contributions (NDCs), which outline their climate action plans. The agreement also includes mechanisms for monitoring progress and providing financial support to developing nations. The other options are incorrect because the Paris Agreement was specifically finalized in 2015. The year 2016 is associated with the agreement entering into force, not its negotiation. Understanding the timeline of global environmental agreements is important in competitive exams and helps in building awareness of international cooperation. Therefore, 2015 is the correct answer as it represents a milestone in climate diplomacy and global environmental governance.

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.

The Rio Earth Summit, formally called the United Nations Conference on Environment and Development (UNCED), was held in June 1992 in Rio de Janeiro, Brazil. It was one of the largest international gatherings focused on environmental issues and sustainable development. The summit produced several key outcomes, including Agenda 21, a comprehensive plan for sustainable development; the Rio Declaration, which outlines principles for environmental protection; and major conventions on climate change and biodiversity. These agreements laid the foundation for modern environmental policy and global cooperation. The summit emphasized the concept of sustainable development, which balances economic growth with environmental protection. It highlighted the responsibility of nations to protect natural resources while promoting development. Other dates listed are incorrect because the conference specifically took place in June 1992. It remains a landmark event in environmental history. Thus, June 1992 is the correct answer, representing a pivotal moment in global environmental awareness and policy-making.

Mastication refers to the process of chewing food in the mouth. It is the first step of digestion, where food is broken down into smaller pieces by the teeth and mixed with saliva. Saliva contains enzymes such as amylase, which begin the chemical digestion of carbohydrates. Chewing also increases the surface area of food, making it easier for digestive enzymes to act. Assimilation refers to the use of absorbed nutrients by the body, absorption is the uptake of nutrients into the bloodstream, and excretion is the removal of waste. Thus, chewing of food is the correct answer. Mastication is essential for proper digestion and nutrient absorption. Understanding digestive processes is important in biology and health sciences.

The International Day to Combat Desertification and Drought is observed annually on 17th June. This day was established by the United Nations to raise awareness about land degradation, desertification, and drought, which affect millions of people worldwide. Desertification refers to the degradation of land in arid and semi-arid regions, often caused by deforestation, overgrazing, poor irrigation practices, and climate change. It leads to reduced agricultural productivity, food insecurity, and displacement of populations. The observance encourages governments, organizations, and individuals to adopt sustainable land management practices. It also promotes international cooperation to address environmental challenges. The other dates mentioned are incorrect because the UN officially designated 17th June for this purpose. Recognizing such international days is important in exams as they reflect global awareness campaigns. Therefore, 17th June is the correct answer, highlighting efforts to combat environmental degradation and ensure sustainable land use.

The human brain is composed of approximately 75% water, making it one of the most water-rich organs in the body. Water is essential for maintaining brain function, including nutrient transport, temperature regulation, and electrical activity. Adequate hydration is crucial for cognitive functions such as memory, concentration, and alertness. Even mild dehydration can impair brain performance. The other percentages are either too low or too high to accurately represent the brain’s composition. Thus, 75% is the correct answer. This emphasizes the importance of water in maintaining overall health and brain function.

Producers, mainly green plants, require nitrogen for synthesizing proteins, nucleic acids, and chlorophyll. However, they cannot directly use atmospheric nitrogen (N₂), which is chemically inert. Instead, they absorb nitrogen in usable forms such as ammonia (NH₃), ammonium ions (NH₄⁺), or nitrates (NO₃⁻). Ammonia is produced through biological nitrogen fixation by certain bacteria, which convert atmospheric nitrogen into a form plants can absorb. This process is crucial for maintaining the nitrogen cycle in ecosystems. CO₂ is used by plants in photosynthesis but does not provide nitrogen. N₂, although abundant in the atmosphere, cannot be directly utilized by plants without conversion. NH₄NO₃ is a fertilizer that provides nitrogen, but the fundamental absorbed form at the biochemical level is ammonia/ammonium. Thus, NH₃ is the correct answer. Understanding nutrient cycles is essential for grasping ecosystem functioning and is a common topic in competitive exams. This concept highlights the importance of microorganisms in supporting plant life and maintaining ecological balance.

Dengue fever is caused by the dengue virus, which is transmitted primarily by the Aedes aegypti mosquito. This mosquito is active during the daytime and breeds in stagnant water. Aedes aegypti is known for its distinctive black and white markings and is commonly found in tropical and subtropical regions. It spreads dengue, chikungunya, and Zika virus. Anopheles mosquitoes transmit malaria, while Culex species transmit diseases like filariasis and West Nile virus. Thus, Aedes aegypti is the correct answer. Preventing mosquito breeding and avoiding bites are key measures to control dengue انتشار.

The pancreas is a vital digestive organ that produces enzymes necessary for breaking down food. These enzymes include amylase (for carbohydrates), lipase (for fats), and proteases such as trypsin (for proteins). The pancreas releases these enzymes into the duodenum, which is the first part of the small intestine. The enzymes travel through the pancreatic duct and mix with bile and partially digested food in the duodenum. This is where most chemical digestion occurs. The environment in the duodenum is alkaline, which is suitable for pancreatic enzyme activity. The stomach primarily performs mechanical digestion and uses acid and pepsin for protein breakdown. The jejunum mainly absorbs nutrients, while the anus is involved in excretion. Thus, the duodenum is the correct answer. Understanding the digestive system’s structure and function is important in biology and helps explain how nutrients are processed and absorbed in the body.

Pepsinogen is an inactive precursor, or zymogen, secreted by the gastric glands in the stomach lining. It is converted into its active form, pepsin, in the presence of hydrochloric acid (HCl). This acidic environment triggers the activation process. Pepsin is a proteolytic enzyme that begins the digestion of proteins by breaking them down into smaller peptides. This process is essential for further digestion and absorption in the small intestine. The conversion of pepsinogen into pepsin is a protective mechanism. If pepsin were active inside the cells that produce it, it could digest the stomach lining itself. By secreting it in an inactive form, the body prevents self-damage. Other options are incorrect: “enzyme” is too general, proteins are the substrate, and amylase digests carbohydrates. Thus, pepsin is the correct answer. This concept is important for understanding enzyme activation and digestive physiology, commonly tested in exams.