Oxygen-15 undergoes beta decay. Which particle correctly completes the equation to show that the numbers of nucleons on the two sides of the
equation are equal?
150 - 15N+ ?

Explanation:

Positron emission: In this process, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino. The beta positive particle released is basically a positron with +1 charge and no mass.

General representation of an element is given as:  

where,

Z represents Atomic number

A represents Mass number

X and Y represents the symbol of an element

For

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.