Which of the following INCREASES the magnetic field at the centre of a circular current-carrying loop?

1. The field at the centre of a single loop is proportional to the current and inversely proportional to the radius. 2. A coil of N turns gives N times the field of a single turn at the centre. 3. So increasing the number of turns multiplies the field directly. 4. Reducing current or increasing radius would reduce the field. 5. An insulator cannot carry the current at all. 6. Hence increasing the number of turns boosts the field at the centre. _Source: NCERT Class 10 Science Ch 13 'Magnetic Effects of Electric Current' (learncbse.in extract)_