CBSE Class 9 Science Chapter 1: Matter in Our Surroundings NCERT Solutions

To convert temperature from Kelvin (K) to Celsius (°C), we use the formula: °C = K - 273.

1. For 300 K:

   $$300\; \backslash text\{\; K\}\; =\; 300\; -\; 273\; =\; 27\; \backslash ,\; ^\{0\}\backslash text\{C\}$$

   So, 300 Kelvin is equal to 27 degrees Celsius.
2. For 573 K:

   $$573\; \backslash text\{\; K\}\; =\; 573\; -\; 273\; =\; 300\; \backslash ,\; ^\{0\}\backslash text\{C\}$$

   Therefore, 573 Kelvin is equal to 300 degrees Celsius.

To convert temperature from Celsius (°C) to Kelvin (K), we use the formula: K = °C + 273.

1. For 25°C:

   $$25^\{\backslash circ\}\backslash text\{C\}\; =\; 25\; +\; 273\; =\; 298\; \backslash text\{\; K\}$$

   Thus, 25 degrees Celsius is equal to 298 Kelvin.
2. For 373°C:

   $$373^\{\backslash circ\}\backslash text\{C\}\; =\; 373\; +\; 273\; =\; 646\; \backslash text\{\; K\}$$

   Hence, 373 degrees Celsius is equal to 646 Kelvin.

1. Naphthalene balls exhibit the property of sublimation. Sublimation is the process where a solid directly transforms into a gas without passing through the liquid state. Due to this property, naphthalene balls gradually vaporize and disappear over time, leaving no solid residue behind.
2. Perfumes are volatile liquids, meaning they vaporize very quickly at room temperature. The resulting perfume vapors are in a gaseous state and spread out rapidly into the surrounding air through a process called diffusion. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. This rapid diffusion allows the scent of the perfume to reach people sitting several meters away.

The increasing order of forces of attraction between the particles is determined by their physical states. Generally, gases have the weakest forces, liquids have intermediate forces, and solids have the strongest forces between their particles.

• Oxygen is a gas at room temperature, so its particles have the weakest forces of attraction.
• Water is a liquid at room temperature, so its particles have stronger forces of attraction than oxygen but weaker than sugar.
• Sugar is a solid at room temperature, so its particles have the strongest forces of attraction among the three.

The physical state of water depends on the temperature:

1. At 25°C, which is well above its freezing point (0°C) and below its boiling point (100°C), water exists as a liquid.
2. At 0°C, water is at its freezing point. At this specific temperature, water exists in equilibrium between its solid state (ice) and its liquid state. Both states can coexist.
3. At 100°C, water is at its boiling point. At this temperature, water exists in equilibrium between its liquid state and its gaseous state (steam or water vapor). Both states can coexist.

1. Water is a liquid at room temperature (approximately 25°C) because:
   • It possesses fluidity, meaning it can flow easily.
   • It has a definite volume but takes the shape of the container it is in (no definite shape). These are characteristic properties of a liquid.
2. An iron almirah is a solid at room temperature because:
   • It is rigid and resists deformation.
   • It has a definite shape and a definite volume. These are characteristic properties of a solid.