Why does wrapping coils around electromagnets make electromagnets stronger?

When the eletric current moves through a wire it makes a magnetic field.  If you coil the wire around and around, it will make the magnetic force stronger, but it will still be pretty weak.  Putting a piece of iron or steel inside the coil makes the magnet strong enough to attract  objects

Explanation:

the dissociation of nickel hydroxide is follows:

the concentration of hydroxide ion is

the equilibrium constant value of nickel hydroxide is = 6.1 * 10^-^1^6 and thus equilibrium equation can be written as:

thus, concentration of ni is 0.23 * 10^-^4 mol /l