Consider the given data.
`{:(,"Half-cell reaction","Standard reduction"),(,,"potential"E^(@)("volts")),(1.,Cr_(2)O_(7)^(2-)+14H^(+)+6e hArr 2Cr^(3+)+7H_(2)O,1.33),(2.,Cr^(3+)+3ehArr Cr(s),-0.74),(3.,Cu^(+)+ehArrCu(s),0.51),(4.,Cu^(2+)+2ehArrCu(s),0.34):}`
The numerical value of the standard cell potential for the reaction, `Cr(s) +3Cu^(+2) rar 3Cu^(+)+Cr^(+3)(aq)` is:

Explanation

`Cu^(+2) +2e hArr Cu(s) 0.34` ...(i)
`Cu^(+)+e hArr Cu(s) 0.51` ..(ii)
eq.(i)-(ii)
`Cu^(+2) +e rarr Cu^(+)`
`E^(@) = 2 xx 0.34 - 0.51 = 0.51`