We're asked to find the number of #"CO"_2# molecules in #1.0# #"kg CO"_2#.
To do this, we can first use the molar mass of #"CO"_2# (#44.01# #"g/mol"#) to find the number of moles of #"CO"_2#:
#1.0cancel("kg CO"_2)((10^3cancel("g CO"_2))/(1cancel("kg")))((1color(white)(l)"mol CO"_2)/(44.01cancel("g CO"_2))) = 22.72# #"mol CO"_2#
Now, we can use Avogadro's number (#6.022xx10^23# #"mol"^-1#) to find the number of #"CO"_2# molecules:
#22.72cancel("mol CO"_2)((6.022xx10^23color(white)(l)"molecules CO"_2)/(1cancel("mol CO"_2)))#
#= color(red)(ul(1.37xx10^25color(white)(l)"molecules CO"_2#
