Thermal Properties of Matter

Pure water freezes at 32°F (0°C) at standard atmospheric pressure. This is the standard freezing point of water. The other temperatures (47°F, 0°F, 19°F) are incorrect - 0°F is very cold (~-18°C), and 47°F and 19°F are above freezing.

The human brain is approximately 80% water by weight. This makes the brain one of the wettest organs in the human body, alongside the heart and lungs. The high water content is essential for proper brain function, including nutrient transport, waste removal, and electrical signal conduction between neurons.

The human brain is approximately 73-80% water, making 80% the most accurate option among the choices provided. Brain tissue has one of the highest water concentrations in the body because of its high metabolic activity and soft tissue composition.

1 Calorie (with capital C) is the heat needed to raise 1g water by 1°C - this is the kilocalorie. 1 calorie (lowercase c) is much smaller. 1 Joule is the SI unit but equals only 0.24 calories.

Pure water freezes at 32°F (0°C) at standard atmospheric pressure. This is the freezing point where liquid water transitions to solid ice. The other temperatures are incorrect for water's freezing point.

Water boils at 212°F (100°C) at sea level under standard atmospheric pressure. This is the temperature where liquid water transitions to water vapor. The other temperatures are incorrect for water's boiling point at sea level.

One calorie is defined as the amount of heat energy required to raise the temperature of 1 gram of water by 1 degree Celsius. This is the scientific definition of the small calorie (cal). Note that 1 Calorie (with capital C, used in nutrition) equals 1000 small calories.

At 0°C, water and ice are in thermal equilibrium - they have the same temperature. The difference is in heat content (enthalpy), not temperature. Water has more internal energy than ice at the same temperature due to the latent heat of fusion.

At Mount Everest's summit (8,848m), atmospheric pressure is about one-third of sea level pressure. This lower pressure reduces water's boiling point to approximately 71°C, though 69°C is the closest option. The exact boiling point varies with weather conditions.

Using the linear scale formula: $T = \frac{L_x - L_{ice}}{L_{steam} - L_{ice}} \times 100$. Here, $\frac{50 - 20}{170 - 20} \times 100 = \frac{30}{150} \times 100 = 0.2 \times 100 = 20$. Thus, the temperature is 20 degrees Celsius.

At high altitudes like Mount Everest, atmospheric pressure is significantly lower, reducing water's boiling point to approximately 69-71°C.

Evaporation is a surface phenomenon that occurs at all temperatures above 0°C, not just at the boiling point. Water molecules escape from the surface when they gain enough kinetic energy, which happens at any temperature. The boiling point (100°C) is when evaporation occurs throughout the liquid volume, not just at the surface. Options A, B, and C incorrectly suggest specific temperatures are required.