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
