Answer: Option (b) is the correct answer.
Explanation:
A covalent bond is defined as the bond which occurs due to sharing of electrons between the combining atoms.
Generally, a covalent bond is formed between non-metals.
For example, both nitrogen and oxygen atoms are non-metals and they combine covalently to form 
compound.
As nitrogen has 5 valence electrons and an oxygen atom has 6 valence electrons. So, there occurs unequal sharing of electrons between the two.
Thus, we can conclude that when a covalent bond forms then electrons in valence shells are shared between atoms.
Single replacement because only one letter is being switched out in the reaction
Answer: The correct option is heterogeneous mixture whose components are attracted differently to a magnet.
Explanation: There are two types of mixtures:
1) Homogeneous mixtures: In these mixtures, the particles are uniformly distributed throughout the mixture. These particles cannot be separated.
2) Heterogeneous Mixtures: These are the mixtures where the particles are visible separated and are not-uniformly distributed. These particles can be separated easily.
If magnet is used to separate the components of a mixture, the heterogeneous mixtures will only get separated.
To separate the components by a magnet, the components of a mixture should attract the magnet differently. One component should attract the magnet and another should not. Hence, they can be easily separated.
The answer to your question is A. Wrought iron because amongst its other properties, wrought iron becomes soft at red heat, and can be easily be forged and forge welded.
