Question

I have lost my pencil. Have you ------------------ to lend me? (do as directed)

Answer 1

Have you an extra one to lend me?  

Have you any to lend me?

It is evident that the blank needs to be filled by something that means 'a pencil'.  However, if we put 'a pencil', it amounts to repetition. This is where we need to use another word for 'pencil'. So, the gap needs to be filled with  'an extra one'.  

'An' is used because it comes before the word 'extra'.  

'Extra' is used because applying common sense, we need to ask for an 'extra' pencil and not the one that the other person is already using.

'One' is another way of referring to a pencil (in this context).  

The word ‘any’ can also be used to convey the same meaning.

Answer 2

Answer:

I have lost my pencil. Have you any to lend me?