The Blood-Brain Barrier (BBB) is a semipermeable membrane that separates blood and the brain. Which choices below would successfully cross the BBB without any help?

water, carbon monoxide gas, Small lipid soluble substances

Explanation:

The BBB is a highly selective semi permeable membrane which prevents the solute in the blood from crossing or passing through the central nervous system of human brain.

It separates the blood from the brain.

In the context,

-- Water successfully crosses the BBB without any help. It can cross through diffusion.

-- carbon monoxide gas can cross BBB. Haemoglobin in blood has 200 times more affinity towards the carbon monoxide when it is compared with oxygen. This is why carbon monoxide poisoning affects the brain.

--- Small lipid soluble substances can also cross BBB without any help.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.