The half-life of lead-212 is 11h. How much of a 100-g sample of lead-212 is left after 33h? Someone please help

Iknow the answer to 13 is b and 14 is d. i just need to know why the correct answers are correct

3.) for each of the following compounds, draw the major organic product of reaction with hcl or naoh and circle whether the starting materials and products will be more soluble in organic solvent or water benzoic acid + hcl: benzoic acid + naoh: oh benzoic acid water/organic water organic fluorenone hс: fluorenone + naoh: fluorenone water/organic water/organic веnzocaine + hci: benzocaine + n»oh: h2n benzocaine water/organic water organic o=

Insoluble sulfide compounds are generally black in color. which of the following combinations could yield a black precipitate? check all that apply. na2s(aq)+kcl(aq) li2s(aq)+pb(no3)2(aq) pb(clo3)2(aq)+nano3(aq) agno3(aq)+kcl(aq) k2s(aq)+sn(no3)4(aq)