How many unpaired electrons are contained in each element: (a) chlorine, (b) selenium, (c) cesium, and (d) phosphorus?

Se-2, Cl-1, Cs-1, P-1

Explanation:

Let us consider the groups the elements belong to

Se- group 16, ns2np4- two unpaired valence electrons

Cl- group 17, ns2np5- 1 unpaired electron

Cs-group 1, ns1- one unpaired electron

P-group 15- ns2np3- three unpaired valence electrons

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2