Answer:
because the number of constitutional confirmation , and geometric isomers goes up with each carbon atom added there are many more possible configurations and connectivities possible with decane , a 10 carbon chain , than with butane, a 4 carbon chain
The answer is four hundred
Lambda = h\ Mv
lambda = 6.624 x 10^-34 / 9.1 x 10^-31 x 2.5 x 10^7
lambda = 2.9 x 10^-11 is your wavelength