O valence electron number is the answer
Get an equal amount of each element by adding coefficients to the different compounds.
Which two solutions, when mixed together, will undergo a double replacement reaction and form a white, solid substance?
1. NaCl(aq) and LiNO3(aq)
2. KCl(aq) and AgNO3(aq) answer
3. KCl(aq) and LiCL(aq)
4. NaNO3(aq) and AgNO3(aq)
2 is the answer because AgCl is formed and that is a white ppt.
A flight simulator that helps astronauts prepare for a shuttle launch is an example of a Scientific Model.