What is the type of bond with δen=1.7? ionic or polar covalent?

Polar. from inter net
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No , it is not necessary that if the E.N difference is greater than 1.7 then the bond should be ionic.For ionic and covalent bonds we see that the bond is between what kind of atoms, they are either metals or non-metals.If the bond is between metal and non-metal then it should be ionic like in NaCl.Na is metal while Cl is non-metal.Na has greater atomic radius can lose electron easily and having low ionization energy while Cl has smaller atomic radius can gain electron easily and having high ionization energy . Therefore they form ionic bond.On the other hand non-metals havimg small atomic radii having high values of I.E therefore non of them can lose electrons due to high ionization energy values.Instead of losing and gaining of electrons they share their valance electrons in order to get stability.Since in HF both H and F are non-metals therefore they form covalent bond.From the above discussion we conclude that whether a chemical bond is between metal and non-metal then it will be ionic and if there is a chemical bond between non-metals it will be covalent.”

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.

The correct answer is b