A galvanometer may be converted into ammeter or a voltmeter. In which of the following cases the resistance of the device so obtained will be the largest?

A galvanometer has resistance $80 \Omega$ and it is shunted with resistance $20 \Omega$. If $20 \%$ of the main current flows through galvanometer, then what is the value of main current?

A cell balances against a length of 150 cm on a potentiometer wire when it is shunted by a resistance of $5 \Omega$. But when it is shunted by a resistance of $10 \Omega$, then balancing length increases by 25 cm . The balancing length when the cell is in an open circuit is

A battery of 6 V is connected to the ends of uniform wire 3 m long and of resistance $100 \Omega$. The difference of potential between two points 50 cm apart on the wire is