A particular substance decays from 500 mg to 100 mg in 180 years. If the decay is exponential, what is the half-life of the substance

the atomic mass is the bottom number on the element.

-steel jelly

i believe the answer is a.

you need to have a picture of the atom that way we can answer it

c is having 4 valence electrons and is bonded to three hydrogens and one sulphur atom, therefore, the number of bond pair is equal to four. as all the valence electrons are used in forming the bonds so, there is no lone pair left on carbon.

s is having 6 valence electrons and is bonded to one other sulfur atom and one carbon atom, therefore, the number of bond pair is equal to 2. as only two valence electrons are used in forming the bonds so, four electrons are left. therefore, two lone pairs are present on s.