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

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.

The 1935 earthquake struck Quetta, now the capital of Balochistan, Pakistan. It occurred on May 31, 1935, with an estimated magnitude of around 7.7, making it one of the most destructive earthquakes in the region’s history. The earthquake caused massive destruction because most buildings were made of mud and were not designed to withstand seismic activity. It is estimated that between 30,000 and 60,000 people lost their lives. The disaster occurred early in the morning, which increased casualties as people were indoors. Quetta lies in a seismically active zone due to the collision of the Indian and Eurasian tectonic plates. This makes the region highly prone to earthquakes. The 1935 event highlighted the need for earthquake-resistant construction and better disaster preparedness. Other cities like Karachi, Lahore, and Jhelum have not experienced such catastrophic earthquakes historically. Therefore, Quetta is the correct answer. This event remains a key example in studies of seismic hazards and urban vulnerability in South Asia.

Attock Fort was built by the Mughal Emperor Akbar in 1581. It is located near the Indus River in present-day Pakistan and was constructed for strategic military purposes. The fort played a crucial role in defending the northwestern frontier of the Mughal Empire against invasions from Central Asia. Akbar was known for strengthening the empire through administrative reforms and military infrastructure. Attock Fort was part of his broader strategy to secure trade routes and maintain control over key regions. Babur founded the Mughal Empire but did not build this fort. Sher Shah Suri was known for road construction, including the Grand Trunk Road, while Aurangzeb ruled later and did not construct Attock Fort. Thus, Akbar is the correct answer. The fort remains an important historical and architectural landmark in Pakistan today.

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.