2.50 g of zn is added to 5.00 g of hcl

Zn+2HCl > 2ZnCl2 + H2

For 2.50 g of Zn

Mass per mol = 2.50/molar mass of Zn = 2.50/65.38 = 0.0382 g/mol
There are two moles of ZnCl2 and total mass = 2*0.0382*molar mass of ZnCl2 = 2*0.0382*136.286 = 10.42 g

For 2 g of HCl

Mass per mol = 2/2*molar mass of HCl = 2/ (2*36.46) = 0.0274 g/mol
For the two moles of ZnCl2, mass produced = 2*0.0274*136.286 = 7.48 g

It can be noted that 2 g of HCl produced less amount of ZnCl and thus it is the limiting reagent.

Particle exchange energy though elastic collision , hope this .