The heating element in an electric iron is made of:
A. nichrome
B. iron
C. constantan
D. tungsten

Hint: Firstly, you could think of the properties that would make a material ideal for being used as a heating element. You could do this by recalling the basic working of these heating elements. Then, you could find which among the given material shows these properties and hence the answer.

Complete answer:
In the question, we are asked to find which among the given materials an electric iron is made up of.
Most of the heating elements are known to be made of Nichrome. We could understand properties of nichrome that makes it ideal for being used as a heating element. Nichrome basically is an alloy made of 80% nickel and 20% chromium. The signature properties of nichrome are: it is corrosion-resistant and has a very high melting point of $1400{}^\circ C$. Apart from these, cost of manufacture is low, strength is high, ductile, is resistant to oxidation, is stable at high temperatures and high resistance makes it more suitable for its application in heating appliances.
The principle behind the working of these heating elements is joule heating. By Joule’s law of heating, we have,
$H={{I}^{2}}Rt$
So, the resistance of the heating element should be high for greater heat to be produced. Also, current when passed through this heating element produces heat by joule heating and thus the material should also have a very high melting point.
To summarize the whole set of points we could say that the nichrome would be ideal among the given options to be used as a heating element in electric iron.

Hence, option A is found to be the correct answer.

Note:
A heating element is used in converting electric energy into heat. This heating is known to happen as the result of the encounter of electric current with resistance. The types of heating elements used may be metals, polymer, thick films, ceramic or semiconductors. We choose nichrome to other metals because even when it is heated to red hot temperature, it develops a chromium oxide layer thereby protecting the heating element from further oxidation.