$,\mathbf{\text{Step}}\mathbf{\text{-}}\mathbf{\text{1:}}\mathbf{\text{Find}}\mathbf{\text{the}}\mathbf{\text{required}}\mathbf{\text{answer}}\mathbf{\text{using}}\mathbf{\text{definition}}\mathbf{\text{of}}\mathbf{\text{co-prime}}\mathbf{\text{numbers.}}$

                   $,\text{By definition of co-prime numbers,}$

                   $,\text{Two numbers having only 1 as,their common factor are called co-prime numbers.}$

                   $,\text{So, HCF of two co-prime numbers is 1.}$

$,\mathbf{\text{Hence,}}\mathbf{\text{the}}\mathbf{\text{correct}}\mathbf{\text{option}}\mathbf{\text{is}}\mathbf{\text{A.}}$