ボールペンのインクがなくなった。

ball-point pen

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

ink

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to be lost (e.g. luggage); to be missing; to be used up; to be run out; to be exhausted; to be consumed; to be reduced to zero; to not occur any more; to disappear (e.g. pain); to be lost (e.g. a dream, confidence)