Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Boron is unable to form $$BF_6^{3-}$$
Reason R: Size of B is very small.
In the light of the above statements, choose the correct answer from the options given below:

We need to evaluate the Assertion and Reason statements.

Assertion A: Boron is unable to form $$BF_6^{3-}$$. This statement is TRUE. Since boron has the electronic configuration 1s² 2s² 2p¹, it possesses only four orbitals in its valence shell (one 2s and three 2p). Therefore, its maximum coordination number is 4 and it cannot accommodate six fluorine atoms. For instance, boron can form $$BF_4^-$$ with coordination number 4 but not $$BF_6^{3-}$$ with coordination number 6, as it lacks d-orbitals in the second shell.

Reason R: Size of B is very small. This statement is TRUE because boron is indeed a very small atom.

From the above, the actual reason boron cannot form $$BF_6^{3-}$$ is the absence of d-orbitals in its valence shell, which restricts its coordination number to 4. Although the small size of boron is correct, it does not explain Assertion A; the unavailability of d-orbitals is the proper explanation.

Therefore, the correct answer is Option B: Both A and R are true but R is not the correct explanation of A.