Which two solutions have similar solubilities at 40°c? na2so4 and nacl na2haso4 and nacl na2haso4 and na2so4 ba(no3)2 and ce2(so4)3 • 9h2o

The correct answer is option C i.e. Na2HAsO4 and Na2SO4 Ba(NO3)2 

Refer to the graph attached below which shows how the solubility of a mixture changes with temperature variation.

As you can see in the graph at 40 °C, both Na2HAsO4 and Na2SO4 Ba(NO3)2  have same solubility coefficients. Thus, the answer is Na2HAsO4 and Na2SO4 Ba(NO3)2 

Outermost (valence) electrons

Rn in the right answer