what happens when two aqueous solutions are combined in a precipitation reaction and no precipitate is formed?  a. the solutions have been neutralized    b. there's no reaction    c. a solubility reaction has taken place    d. an acid-base reaction has taken place

There's no reaction for me.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

3. dark matter

empty space could also be a simple vacuum