All questions of The Amazing World of Solutes, Solvents, and Solutions for Class 8 Exam

Understanding the Effect of Pressure on Gas Density
When discussing gases, it's essential to understand how pressure influences their density.
What is Density?
- Density is defined as mass per unit volume. For gases, it is typically expressed in grams per liter (g/L).
How Pressure Affects Density
- When the pressure on a gas increases, the gas molecules are forced closer together.
- This results in a decrease in volume, leading to an increase in density.
Reason Behind the Change
- According to Boyle's Law, at constant temperature, the volume of a gas is inversely proportional to the pressure applied.
- As pressure rises, the volume decreases, and since density equals mass divided by volume, a smaller volume with the same mass results in higher density.
Practical Examples
- Consider a balloon: when you squeeze it, you increase the pressure inside, causing the gas molecules to pack more tightly, thus increasing density.
- In the atmosphere, higher pressure at sea level leads to denser air compared to higher altitudes where the pressure is lower.
Conclusion
- In summary, increasing pressure on a gas leads to an increase in its density, making option 'D' correct. This principle is crucial in various scientific and practical applications, such as understanding weather patterns and designing pressurized containers.

Understanding Density Units for Liquids
Density is a measure of how much mass is contained in a given volume of a substance. It is an important property for liquids and is commonly expressed in various units.
Common Units for Density
1. kg/m³ (Kilograms per Cubic Meter)
- This is the SI (International System of Units) unit for density.
- It is commonly used in scientific contexts, particularly in physics and engineering.
2. g/mL (Grams per Milliliter)
- This unit is widely used in chemistry and biology.
- Since 1 mL is equivalent to 1 cm³, this unit is particularly convenient for measuring the density of liquids in small volumes.
3. g/cm³ (Grams per Cubic Centimeter)
- This is another common unit for expressing density, especially for liquids.
- It is equivalent to g/mL and is often used in laboratory settings.
Why All Units are Correct
- All mentioned units (kg/m³, g/mL, g/cm³) convey the same concept of density but are used in different contexts depending on the field of study or the scale of measurement.
- For instance, in everyday situations, g/mL or g/cm³ is more practical, while kg/m³ is more suitable for larger volumes.
Conclusion
Thus, the answer is option 'D' because density can indeed be expressed in all of these units, making them relevant and interchangeable based on the application and context. Understanding these units helps in accurately describing the properties of liquids in both practical and theoretical scenarios.