To how much water should 250 mL of 12 M hydrochloric acid be added to
produce a 4.0 M solution?

500 mL water

Explanation:

M1V1 =M2V2

M -molarity, V - volume of solution before adding water

M1 = 12MV1 = 250 mL

M2 = 4.0 M

12M * 250 mL = 4.0*V2

V2 = 12*250/4.0 = 750 mL of solution  should become after adding water

750 mL - 250 mL = 500 mL of water should be added

c.

explanation:

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.