Which of these chains has the lowest number for the carbon atom carrying the branch?

Which of the following has the largest number of atoms?

Number of carbon atoms in the main chain.

Which contains the same number of atoms as in 6g carbon?

Which of the following acids has the lowest value of dissociation constant?

Best method for preparing aliphatic primary amines from alkyl halides without changing the number of carbon atoms in the chain is

In which of the following reactions, the number of carbon atoms does not decreases