Learn Farsi: حدود ده ردیف خالی باقی است.

The word hodud literally relates to limits or bounds, but here it acts as a marker for approximation meaning about. It must connect to the number that follows it using an ezafe (a short 'e' sound). So, we say hodud-e dah to mean about ten.

Could we use taghriban instead of hodud-e to mean about here?

Yes, you can use taghriban. However, the grammar changes slightly. Because taghriban is an adverb, it does not take an ezafe. You would just say taghriban dah radif instead of using the connecting 'e' sound.

Why is the word radif (row) in the singular form when the sentence is talking about ten of them?

This is a strict and important rule in Farsi: nouns that come immediately after a specific number are always kept singular. Even though there are ten rows, you must say dah radif (ten row) rather than pluralizing it to dah radif-ha.

Since the sentence is about multiple rows, why does it end with the singular verb ast (is) instead of a plural verb?

In Farsi grammar, inanimate subjects (things that are not alive, like empty rows) generally take a singular verb, even if the quantity is plural. Therefore, the singular ast is perfectly natural here rather than a plural verb like hastand.