Questions

The Ozone layer which is present in the Earth's atmosphere protects it by restricting from UV or Ultraviolet radiation, the dangerous rays contained by Sun.

‘Unless’ is used to denote the condition i.e. ‘If’...... ‘Not’. So, again the use of negative word ‘not’ is superfluous. So, the phrase, ‘are not very’ needs to be replaced with ‘are very’ to make the sentence grammatically correct. Thus, the correct formation would be, ‘Unless, you are very careful, you will run into debt’.

When water freezes its density decreases.

Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at about 4°C it reaches a maximum density and then decreases in density as it approaches the freezing point.