Which suffix indicates a quality or condition in the words remarkable and inhospitable?

The choice of -able as the correct suffix is based on its function in the formation of adjectives that convey a quality or condition. In the word "remarkable," the suffix -able transforms the root "remark" into an adjective, indicating something that is worthy of being remarked upon or is notable in quality. Similarly, in the word "inhospitable," the suffix -able helps indicate a quality related to the root "hospit," which pertains to hospitality. Here, -able signifies that the subject lacks a welcoming condition, thus showing how the suffix conveys a particular quality related to the core word.

While the other suffix options provided serve different grammatical functions, they do not convey the same quality or condition aspect present in these particular words. For example, -ing typically creates participles and gerunds rather than adjectives, -ed relates to past participles, and -ness usually denotes a state or condition but is not applicable in the examples given. Therefore, -able is the appropriate choice to illustrate the quality or condition in the selected words.