Which has the larger first ionization energy—magnesium or phosphorus? a

Phosphorus has the greater first ionization energy.

b

Magnesium and phosphorus have equal first ionization energies.

c

Magnesium, but not phosphorus, has a measurable first ionization energy.

d

Magnesium has the greater first ionization energy.

The correct option is a

Explanation:

First ionization energy is the minimum amount of energy required to remove the most loosely bound electron (valence electron) from the outermost shell of a gaseous or neutral atom. Since it takes more amount of energy to remove more electrons, it (ionization energy) generally increases across the period and decreases down a group because the closer the outermost shell is to the nucleus, the more difficult/energy required to remove electrons in that shell.

Since magnesium and phosphorus are on the same period (period 3), it can be deduced from the explanation above that phosphorus has a greater first ionization energy than magnesium because phosphorus (5 valence electrons) has more electrons in it's outermost shell than magnesium (2 valence electrons).

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current