How to distinguish between CsCl and NH4Cl by a chemical test? $\ce{CsCl}$ and $\ce{NH4Cl}$ have similar reactions. For example, they can react with $\ce{AgNO3}$ to produce $\ce{AgCl}$ precipitate.
So my question is:  


  Can we use a chemical test to distinguish between solid $\ce{CsCl}$ and $\ce{NH4Cl}$?  




The $\ce{Cs+}$ ion is very unreactive and I do not know any reactions involving it. I believe the chemical test can somehow convert the $\ce{NH4+}$ ion into $\ce{NH3}$ gas so that we can test it with a moist red litmus paper.
Correct you can distinguish them by their reaction with a base. You should use a base, such as $\ce{NaOH}$. $\ce{Cs^+}$ wouldn't react with $\ce{NaOH}$, while $\ce{NH4+}$ will undergo reaction $$\ce{NH4+ + OH- -&gt; NH3 + H2O}$$ $\ce{NH3}$ is a gas and can be detected with a moist litmus paper.

If you will, you can actually detect $\ce{Cs+}$ using a procedure from this paper:

"Selective Detection of Cs+ in Water Solutions via One-Step Formation of a New Type of Struvite-Like Phosphate". However, this is an exotic reaction (in practice you would use the flame color test) and you don't have to do it since you only need to distinguish samples.