115. Calculate the mass of each of the following amounts. a. 3.00 mol of selenium oxybromide, SeoBr2
b. 488 mol of calcium carbonate, CaCO3
c. 0.0091 mol of retinoic acid, C20H2O2
d. 6.00 x 10-8 mol of nicotine, C10H14N2
e. 2.50 mol of strontium nitrate, Sr(NO3)2
f. 3.50 x 10-6 mol of uranium hexafluoride, UF6

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).

The answer is  d.  hydrogen 

  the volume of  0.220 m k2s    solution  required  to  completely  react with 175 ml  of 0.115m co(no3)2  calculate the moles  of co(no3)2 =  molarity x volume/1000175 x0.115/1000= 0.02  moleswrite  the reacting  equationk2s(aq)  +  co(no3)2  = 2 kno3(aq)  + cos(s)by  use  of mole ratio between k2s to co(no3)2 which  is  1: 1 the moles of k2s is therefore = 175  x0.115/1000= 0.02  molesvolume = moles/molarity=0.02/0.22=0.09  ml  of k2s