[tex]\qquad \qquad\huge \underline{\boxed{\sf Answer}}[/tex]
Here's the solution ~
[tex]\qquad \sf \dashrightarrow \: (3 {a}^{2} {b}^{4} )( - 8a {b}^{3} )[/tex]
[tex]\qquad \sf \dashrightarrow \: (3 \times - 8)( {a}^{2} \times a)(b {}^{4} \times {b}^{3} )[/tex]
[tex]\qquad \sf \dashrightarrow \: - 24( {a}^{3} )( {b}^{7} )[/tex]
[tex]\qquad \sf \dashrightarrow \: - 24 {a}^{3} {b}^{7} [/tex]
So, The Correct choice is D
