Question

Which of the following statements is not true for halogens?
A. All form monobasic oxyacids.
B. All but fluorine show positive oxidation states.
C. All are oxidizing agents.
D. Chlorine has the highest electron-gain enthalpy.

Answer 1

HOF breaks into fluorine and oxygen. So we cannot say that all form monobasic oxyacids. We know that fluorine shows some anomalous behavior because of the smaller atom. Chlorine has the highest electron-gain enthalpy due to electron repulsion domination nature which is highest in chlorine and smaller in fluorine.

Complete step by step answer:
According to the question, the first statement says that all halogens form monobasic oxyacids. But we know that a compound HOF, Which is not stable but exists. HOF breaks into fluorine and oxygen. So we cannot say that all form monobasic oxyacids.
All halogens form monobasic oxyacids except HOF.
In the second statement we have, all but fluorine show positive oxidation states. We know that fluorine shows some anomalous behavior because of the smaller atom.
In the third statement all are oxidizing agents. We know that all the octets we have are incomplete. The reason behind it required one more electron to be in its stable state. Hence gets a stable configuration. That’s why they always gain electrons.
That’s why they are oxidizing agents.
In the fourth statement we have chlorine has the highest electron- gain enthalpy. Chlorine has the highest electron-gain enthalpy due to electron repulsion domination nature which is highest in chlorine and smaller in fluorine.
Hence from all the statements it is clear that the statement A is the false statement.

So, the correct answer is Option A.

Note: Electron- gain enthalpy is the amount of energy released in the isolated gaseous atom while addition of an electron. Nuclear force applied on the electron due to this become less. Chlorine has the highest electron-gain enthalpy due to electron repulsion domination nature which is highest in chlorine and smaller in fluorine.