Which chemical does blood–brain and csf–brain barrier control with easy entrance?

The blood-brain barrier and the cerebrospinal fluid (CSF) brain barrier, provides the means for maintaining the stable chemical environment of the brain. Only water, Carbon dioxide, and oxygen enter the brain with ease. The purpose of the blood-brain barrier is to protect against circulating toxins or pathogens that could cause brain infections, while at the same allowing the chemicals and vital nutrients to reach the brain.

Explanation:

Oxygen

Explanation:

There are few chemicals that have easy access to the brain through the two barriers, the blood-brain barrier and the cerebrospinal fluid (CSF)-brain barrier, and they are only water, carbon dioxide, and oxygen.  

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).