Tag: science & technology

Most of Earth's accessible freshwater is stored in underground aquifers (groundwater), which account for about 30% of all freshwater. While glaciers and ice caps hold more freshwater overall, they are not accessible for human use. Aquifers represent the largest source of accessible liquid freshwater.

According to WHO and UNICEF reports, approximately 17% of the global population lacks access to safely managed drinking water services. This represents over 1 billion people without reliable access to clean water, making it a critical global health and development issue.

Oil is hydrophobic, meaning it repels water and does not mix with it. This property is due to oil's nonpolar molecular structure, which cannot form hydrogen bonds with polar water molecules. This is why oil and water separate into distinct layers when mixed.

Cohesion is the property of water molecules sticking to each other through hydrogen bonding. This is different from adhesion (sticking to other surfaces). Cohesion gives water its high surface tension and allows for phenomena like water droplets forming spherical shapes and capillary action in plants.

Evaporation is the phase change where liquid water gains thermal energy and transforms into water vapor (gas). This process is primarily driven by solar energy heating surface waters like oceans, lakes, and rivers. Evaporation is a fundamental step in the water cycle that returns water to the atmosphere.

The human body is approximately 60% water by weight. This percentage varies slightly by age (infants are about 75% water), gender, and body composition (lean body mass has more water than fatty tissue), but 60% is the widely accepted average for adult humans. Water is essential for nearly all bodily functions.

Surface tension is the cohesive force between water molecules that causes them to minimize surface area, creating droplet shapes. On waxy (hydrophobic) surfaces, water cannot spread out due to weak adhesive forces, so surface tension dominates and forms beads. Capillary action would actually pull water into narrow spaces, which is the opposite of beading.

Coagulation is the initial step in water purification where chemicals (like alum) are added to neutralize charges on suspended particles, causing them to clump together into larger particles called floc. This is necessary because the particles are too small to settle on their own. Sedimentation follows coagulation - it's where the heavy floc settles to the bottom. Aeration adds oxygen and distillation is a completely different process involving boiling and condensation.

Water is a polar molecule because oxygen is highly electronegative and pulls electron density toward itself, creating a partial negative charge on the oxygen side and partial positive charges on the hydrogen sides. Option A is the opposite of reality. Option C is incorrect because water IS polar - this uneven charge distribution is why water dissolves many substances and forms hydrogen bonds.

The Manhattan Project was the code name for the US research and development effort to produce nuclear weapons during World War II. It began in 1942 and involved over 130,000 people at secret sites across the US.