The formula of nitric acid is HNO₃.

In nitric acid, the colour observed is red, which can also be shades of orange or yellow. In ammonia solution, the colour is blue.

The correct row is D, which indicates a change from pH 10 to pH 2.

To calculate the percentage by mass of oxygen:

1. The molar mass of ammonium nitrate (NH₄NO₃) is calculated as:

   • H: 4 × 1 = 4
   • N: 2 × 14 = 28
   • O: 3 × 16 = 48

   Total = 4 + 28 + 48 = 80 g/mol

2. The total mass of oxygen is 48 g.

3. Using the formula for percentage by mass: ext{Percentage by mass of oxygen} = rac{ ext{Mass of oxygen}}{ ext{Total mass}} imes 100

   Thus, percentage = (48/80) × 100 = 60%.

Method to Investigate Temperature Changes

Equipment Needed

• Suitable container or beaker
• Thermometer
• Ammonium nitrate
• Water
• Stirring rod or spatula

Steps

1. Use a suitable container for the test.
2. Use insulation to maintain stable temperatures.
3. Add water to the container, noting the initial water temperature using a thermometer.
4. Add a stated mass (e.g., 1 g or 1 spatula) of ammonium nitrate to the water.
5. Stir the solution to ensure the ammonium nitrate dissolves completely.
6. Measure the final temperature after dissolution, recording the lowest or highest temperature observed.
7. Calculate the temperature difference and graphically represent this data.
8. Repeat with different masses of ammonium nitrate, and repeat steps to maintain water volume.

This investigation will help in understanding how temperature varies with the quantity of ammonium nitrate dissolved.