Atomic number of which of the following elements is greater than that of Copper?

If the pH value of a substance is lower than 7, it would be considered as–

Which of the following is the strongest hydracid known?

Which acid is used in lemons? 

In 1931, who recognised that an aromatic compound must have an odd number of pairs of electrons, which can mathematically be written as 4n+2 (n = 0,1,2,3 etc.)?

Curie is the unit of: 

Which of the following energy is most used in organic quantities?

Which gas is known as 'noble gas' ?