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Answer: cycloaddition of 1,3-butadiene and allyl anion is thermally allowed.
Explanation:
Using the frontier molecular orbital approach, we consider if the symmetry of the LUMO of the diene (1,3-cyclobutadiene) and the HOMO of the dienophile allyl anion), match each other since the diels alder reaction is a symmetry allowed process. The symmetries of these frontier molecular orbitals match each other hence the reaction is thermally allowed. It should be notes that 4+2 cycloadditions are thermally allowed although they are slow.
 
        
             
        
        
        
Amino acids combine to form a dipeptide molecule, but their reaction is a condensation reaction. 
        
             
        
        
        
Balanced chemical  equation  is
3CaCl2 +2Na3PO4-->6NaCl +Ca3(PO4)2
moles of  CaCl2  =89.3g/[ (35.5x2) +40]=0.805moles
from  the  equation  above  the  ratio  of  CaCl2  to  Ca3(PO4)2  is  3:1  therefore  the  moles  of Ca3(PO4)2  is 0.809/3=0.268moles
mass  is  therefore  0.268  x310.18(R.F.M of   Ca3(PO4)2 ) =83.23grams
        
             
        
        
        
The products and reactants weigh the same since u have to balance out the equation to have an equal number of molecules on bothsides