The correct answer is option 3: 2 and 4 only.
Let`s discuss each option to understand why it is correct or incorrect.
Option 1: In this option, Helium is mentioned as a liquid at room temperature and standard pressure. However, Helium is actually a gas at room temperature and standard pressure, so option 1 is incorrect.
Option 2: This option includes Mercury, Chlorine, and Bromine as elements that are liquids at room temperature and standard pressure. Mercury is indeed a liquid at room temperature and standard pressure, so this part of the option is correct. However, both Chlorine and Bromine are actually gases at room temperature and standard pressure. Therefore, option 2 is incorrect.
Option 3: In this option, Mercury and Bromine are mentioned as elements that are liquids at room temperature and standard pressure. Both Mercury and Bromine are indeed liquids at room temperature and standard pressure, so this option is correct.
Option 4: This option includes Helium and Chlorine as elements that are liquids at room temperature and standard pressure. As discussed earlier, Helium is actually a gas at room temperature and standard pressure. Therefore, option 4 is incorrect.
In summary, the correct option is 2 and 4