TargetIIT

1)gallium forms GaCl[ss]2[/ss]. this is because
a)large size of gallium
b)very high hydration energy of Ga(III) ion.
c)gallium can form both univalent and trivalent ions.
d) high electronegativity of chlorine.

2)which is stronger reducing agent cr[p]+2[/p] or fe[p]+2[/p] ?

the answer is C..looks like a previous JEE quesdtion...
it's a nice one to confuse the student as here Ga seems to be in +2 oxidation state..but the actual formula is Ga[p]+[/p][GaCl4][p] - [/p] in which one Ga is in +1 oxidation state and the other in +3 oxidation state...

e.c of Fe[p]2+[/p] = d[p]6[/p] system loses an electron to change to stable d[p]5[/p] system (full filled t2g considering that pairing occurs)

e.c of Cr[p]2+[/p] = d[p]4[/p] system so ......

on losing an electron changes to d[p]3[/p] system..(half filled t2g)

now which one is more stable half filled or full filled ???? confused!!!

[2]

@Sandipan..well i guess we see the reducing character in presence of H[ss]2[/ss]O..i mean aqueous solutions..so pairing will not occur..in case of Fe[p]3+[/p] it will be t[ss]2g[/ss][p]3[/p] e[ss]g[/ss][p]2[/p] ..and in case of Cr[p]3+[/p] it will be t[ss]2g[/ss][p]3[/p]..so the second one is more stable....

[hide]Cr[p]3+[/p] one is more stable coz it has more negative CFSE as compared to Fe[p]3+[/p][/hide]

or maybe in simpler words...

Cr can go upto +6 state whereas Fe can go till +3 only...so Cr should be better reducign agent..

okk..end to all debate..i got my ans
                     oxidn potential
Cr3+ + 3e- = Cr 0.74
Fe2+ + 2e- = Fe 0.41

To tell which is the strongest reducing agent,The bigger the oxidation potential. , the stronger the reducing agent.

Good..[1]