Learn Croatian: Bio sam bespomoćan bez mobitela. - I was helpless without a mobile phone.

The adjective is built from the prefix bez- (without), the root word pomoć (help), and the adjective suffix -an. When the voiced consonant z in bez- attaches directly to the voiceless consonant p in pomoć, voice assimilation occurs. The voiced z changes to its voiceless counterpart s, giving us bespomoćan.

Since the preposition bez also means 'without', why doesn't its spelling change when placed before other words?

bez is an independent preposition here, not a prefix attached to a word. In standard Croatian spelling, voice assimilation only changes the spelling within a single merged word (like the prefix in bespomoćan). Separate words keep their original spelling, even if they end up next to a voiceless consonant in a sentence (for example, bez problema).

Why is the word for mobile phone written as mobitela?

The preposition bez strictly requires the noun following it to be in the Genitive case. Because mobitel is a masculine noun ending in a consonant, its Genitive singular form is made by adding -a.

Why use the short form bespomoćan instead of the longer form bespomoćni?