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Three half lives meant that the mass was halved three times. Therefore, 20 * 2 * 2 * 2 to reverse the process yields 160 grams in the beginning.
A and b are related because if u look carefully at what its showing u that there both the same but what its telling u is not the same.
a and c are the same but the picture is different and also the way they describe it is different and what they want u to look at is that if you look at it closely then youll know the difference and how to find it as well
“Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.”
https://www.chemguide.co.uk/atoms/bonding/electroneg.html
^this link may help you understand. Good luck!
<u>Body systems associated with gases(</u>particularly that which was asked<u>):</u>
• Respiratory System.
• Cardiovascular System or Circulatory System or Vascular System.
<em>Note: All these three are the names of the same thing i.e cardiovascular system, circulatory system and vascular system.</em>