(ii) What is the significance of temperature t°С?

This is the temperature scheme that astronomers use to measure the heat in distant objects such as the sun's corona or the gas and dust between stars. There are three temperature scales in common use today: kelvin (K), centigrade or Celsius (C), and Fahrenheit (F).

thats how its supposed to be

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.