A chemical bond that involves the transfer of electrons from a metal to a nonmetal and thus forms ions and the atoms in the molecule are attracted towards each other through electrostatic force of attraction are said be ionic bond. In short, the bond formed between the two oppositely charged ions.
In salt, the compound formed between sodium and chlorine is sodium chloride having molecular formula 
where sodium is a metal and chlorine is the non-metal. The formation of the compound takes place by transfer of an electron from sodium thus forming a cation of formula 
to chlorine which gains electron and thus results in an anion formation having formula 
. The force of attraction between these oppositely charged ions that helds them together and results in formation of compound is electrostatic force of attraction.
Hence in salt, the nature of bond between sodium and chlorine is ionic.
Need a picture for reference
I believe the answer is B. Definitely not D or A, and C doesn't makes sense.
Compound Formula CuF2
Appearance White crystalline powder
Melting Point 836° C (1,537° F)
Boiling Point 1,676° C (3,049° F)
Density 4.23 g/cm3
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To understand what makes a material hard, it is necessary to look at the atomic structure of its crystals. ... In diamonds, however, the carbon atoms are bound together in a tetrahedral formation, a shape that is extremely rigid. Combined with the strong carbon to carbon bonds, it makes diamond extremely hard
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