The electromagnet shown below is made up of a coil of electrical wire wrapped around an iron core.

which of the following would decrease the strength of this electromagnet?

a adding batteries to the circuit
b removing its iron core
c increasing the current through the coil
d increasing the number of wire loops in the coil

B. Removing its iron core

Explanation:

In an electromagnet role of its core is very important as it concentrate magnetic flux to make magnetic field more powerful. Generally core of electromagnet is made up of a ferromagnetic material or of a ferrimagnetic material such as iron. Adding batteries to the circuit and increasing the current through the coil and increasing loops in the coil will increase magnetic  strength of an electromagnet.

its c i just checked it