Given that `E_("Al^(3+)|Al)^(@)=-1.66V, E_(Cd^(2+)|Cd)^(@)=-0.40V, E_(Pb^(2+)|Pb)^(@)=-0.126V and E_(Zn^(2+)|Zn)^(@)=-0.76V`, arrange `Al, Cd, Pb and Zn` in increasing order of their reactivity.

Explanation

Metals having lower standard reduction potential will have higher tendency to get oxidised and thereby have higher reactivity. The order of increasing standard reduction potential of the given electrodes is : `E_(Al^(3+)|Al)^(@)ltE_(Zn^(2+)|Zn)^(@) lt E_(Cd^(+)|Cd)^(@)ltE_(Pb^(2+)|Pb)^(@)`. Hence the order of increasing reactivity is : `Pb lt Cd lt Zn lt Al.`