A resistance of `2Omega` is connected across one gap of a metre - bridge (the length of the wire is 100 cm) and an unknown resistance, greater than `2Omega,` is connected across the other gap. When these resistances are interchanged, the balance point shifts by 20 cm. Neglecting any corrections, the unknown resistance is
`3 Omega`
`4 Omega`
`5 Omega`
`6 Omega`