Hi Maha You might be better to ask this question in the Spanish language part of italki, as you will have more chance of contacting Spanish speakers. I do not speak Spanish, but I think it may be because it changes the sounds of other letters. I know this is the case in Italian. For example the letter 'c' followed by an 'i' has a sound a bit like the English 'chur' in the word 'circa', but the letter 'c' followed by 'h' and then 'i' in the word 'chiave' sounds more like 'key' in English - so the sounds of both the 'c' and 'i' have been changed by the 'h'. If there are any Spanish speakers out there can you confirm if this correct??

Thank you Madam , for your valuable information ,sure I will check that link now .

Hi, Maha, as John wrote, this is due to language change. When Latin got to the Iberian Peninsula, it slowly modified. One feature that appeared was a shift of /f/ to /Ø/ (null). This is not a strange shift because it is a clear case of consonant weakening (lenition) from a labial or labiodental sound to its eventual disappearance. You can compare modern Portuguese and Spanish to see some cases where Portuguese retained /f/ when it was lost in Spanish, such as in fazer/hacer, farinha/harina, falar/hablar, filho/hijo. There's more to it, of course. If you're interested, check out an overview at https://www.staff.ncl.ac.uk/i.e.mackenzie/cons.htm. Otherwise, just google "Spanish lenition h".

Nice examples Sir , thank you so much .