Question

Should the resistance of ammeter be low? Give reason.

Answer 1

The work of an ammeter is to measure the current.So, if you connect an ammeter with a large resistance then it increases the resistance of the circuit and thus decreasing the amount of current flowing through the circuit.

Answer 2

Yes, ideally the resistance of the ammeter should be zero but since that is not possible, it is kept to the lowest value possible.
The ammeter is used to measure strength of current which is the the ordered flow of charges. So, if its resistance is high, it will not allow the charges to move freely and hence will give a lower value of the current in the circuit.