Answer
The ionic compound formed would have the chemical formula $$CsCl$$
Work Step by Step
The electron configuration of cesium ($Cs$) is $$[Xe]6s^1$$
The electron configuration of chlorine ($Cl$) is $$[Ne]3s^23p^5$$
Both of these atoms would tend to lose, gain or share electrons so that it could reach an octet, that is to have 8 valence electrons, or in other words, to achieve the configuration of a noble gas.
$Cl$ atom lacks only 1 more electron to reach an octet $(2s^22p^6)$, and $Cs$ atom, if loses 1 valence electron in subshell $6s$, would achieve the configuration of noble gas $Xe$, with 8 valence electrons (an octet).
Therefore, $Cs$ atom is willing to lose 1 electron, and $Cl$ atom is willing to accept that electron from $Cs$ atom, so that both can achieve an octet.
Eventually, there is 1 $Cs$ atom and 1 $Cl$ atom involved in the reaction. That means the ionic compound formed would have the chemical formula $$CsCl$$
