In the following question, select the one word that best substitutes the given phrase: “Costing nothing.”

Introduction / Context:
This vocabulary question asks you to replace a descriptive phrase with a single word in English. The phrase is “costing nothing.” The goal is to identify the standard word that means something is free of charge. Such one word substitution questions check whether you can connect clear definitions to concise terms that occur frequently in formal reading passages and instructions, such as on tickets, advertisements or notices.

Given Data / Assumptions:

• The phrase “costing nothing” means something is provided free of charge with no payment required.
• Gratis is an English word borrowed from Latin which means “free” or “without charge.”
• Fortis generally refers to being strong and is used in specialised linguistic or medical contexts, not about price.
• Glottis refers to a part of the larynx in anatomy, connected with the vocal cords.
• Abatis refers to a field fortification made of felled trees, not a monetary idea.
• We must select the word that directly expresses the idea of being free of cost.

Concept / Approach:
To solve one word substitution questions, break the phrase into its core concept and check which option is the standard concise term. The phrase here contains the idea of cost and the fact that the cost is zero. Therefore, the correct word must be one that speakers use to describe “free of charge” conditions. The other options are deliberately chosen technical or unrelated words set as distractors. Knowing basic roots and common Latin borrowings like gratis can significantly improve performance in such vocabulary items.

Step-by-Step Solution:
Step 1: Understand the phrase. “Costing nothing” clearly indicates that you do not have to pay for the item or service. Step 2: Evaluate the option Gratis. This word is widely used to mean “for free,” “without payment,” or “free of charge,” for example, “The brochures were given gratis to visitors.” It therefore matches the phrase exactly. Step 3: Check Fortis. This word does not relate to price. In linguistics, it can refer to strong articulation of a consonant, while in Latin it simply means strong. It does not mean free. Step 4: Check Glottis. This is an anatomical term describing part of the voice box, dealing with sound production in the throat. It has no connection with money or cost. Step 5: Check Abatis. This word denotes military obstacles or fences made from felled trees. Again, it is unrelated to the idea of cost or price. Step 6: Since only Gratis expresses the idea of costing nothing, it is the correct option.

Verification / Alternative check:
To verify your choice, imagine replacing the phrase in a sentence. “Entry to the museum is gratis” clearly means entry is free. Substituting Fortis, Glottis or Abatis would make the sentence nonsensical. You can also recall that many shops or services use the phrase “items are given gratis” in notices, clearly meaning given without payment. This confirms that Gratis is standard usage for “costing nothing.”

Why Other Options Are Wrong:
Fortis, Glottis and Abatis are all technical terms from different fields. Fortis is related to strength or strong articulation, Glottis is connected to anatomy of the throat, and Abatis is a military fortification of felled trees. None of these words carry the meaning of something being free of charge. Choosing any of them would therefore completely change the sense of any sentence in which they replaced the phrase “costing nothing.”

Common Pitfalls:
Candidates sometimes misread such questions and look for a word that merely sounds similar to English “gratis” or “grateful.” It is important to focus on the meaning provided by the phrase, not on the sound patterns of the options. Another common pitfall is unfamiliarity with borrowed Latin terms used in English. Building a small mental list of common Latin words such as gratis, per annum, and versus can give a helpful advantage in vocabulary questions across exams.

Final Answer:
The correct one word substitute for “costing nothing” is Gratis, so the correct answer is option Gratis.