A number of substances can exist as solid, liquid, or gas depending on the temperature.
Water is the most common among these substances. When the temperature is less than 0 degrees Celcius, the water exists as ice (solid). The ice melts at 0 degrees Celcius and converts to water (liquid). Water stays in the liquid form till the temperature rises to 100 degrees Celcius, beyond which it exists as water vapor (gas). Thus, water can exist as a solid (ice, temperature < 0 degrees Celcius), liquid (water, temperature between 0 degrees Celcius and 100 degrees Celcius), and gas (water vapor, temperature > 100 degrees Celcius).
Some other examples can be iron, oxygen, etc. Iron is solid at room temperature and converts to the liquid state at 2800 degrees Fahrenheit and the gaseous state at 5182 degrees Fahrenheit. Similarly, oxygen, which is a gas at room temperature, converts to the liquid state at -297 degrees Fahrenheit and the solid state at -362 degrees Fahrenheit.
Hope this helps.