Answer:
10.5 mole
Explanation:
Data given:
no. of mole xenon hexafluoride = 10.5 moles
no. of mole cesium fluoride  = 11 moles
moles of CsXeF₇ = ?
Reaction Given:
     CsF(s) +  XeF₆(s) ---------> CsXeF₇(s)
Solution:
First we will look for the reaction
        CsF(s) +  XeF₆(s) ---------> CsXeF₇(s)
if we look for the mole ratio of CsF to XeF₆
       CsF(s)  +  XeF₆(s) ---------> CsXeF₇(s)
        1 mole    1 mole
It means there is 1:1 that is one mole of  CsF combine 1 mole XeF₆ to form CsXeF₇. So if we look at the given data cesium fluoride is in excess than XeF₆
Excess amount of CsF = 11.0 mole - 10.5 mole = 0.5 mole
So XeF₆ is limiting reactant and formation of product depends on the amount of XeF₆.
So again look at the reaction on the base of limiting reactant
        CsF(s)  +  XeF₆(s) ---------> CsXeF₇(s)
                  1 mole         1 mole
it means 1 mole XeF₆ produces 1 mole of CsXeF₇, then how many moles of CsXeF₇ will be produce from 10.5 moles of XeF₆
Apply unity formula
         1 mole XeF₆ ≅ 1 mole of CsXeF₇
         10.5 mole XeF₆ ≅ X mole of CsXeF₇
Do cross multiplication
       mole of CsXeF₇ =  10.5 mole x 1 mole / 1 mole
       mole of CsXeF₇ =  10.5 mole
So,
10.5 mole of CsXeF₇ will be produces.
