To solve this question, the user needs to know the correct verb tense to use when making predictions or describing future events. In this case, the sentence is describing a future event (his arrival) that will trigger a subsequent action (him giving a call).

Now, let's go through each option and explain why it is right or wrong:

A. will arrive: This option is incorrect because it uses the future simple tense (will arrive) to describe a future event. While this tense is often used to make predictions or describe future actions, it is not the best choice in this context because the sentence already includes the time indicator "as soon as," which implies that the event is imminent or very close to happening. Therefore, we need to use a more immediate verb tense.

B. arrives: This option is correct. The present simple tense (arrives) is the most appropriate verb tense to use in this context because it is used to describe habitual actions or actions that are happening at the moment of speaking. In this case, the sentence is describing a future event that is very close to happening (as soon as he arrives), so the present simple tense is the most appropriate choice.

C. is arriving: This option is incorrect because it uses the present continuous tense (is arriving) to describe a future event. While this tense is often used to describe actions that are in progress at the moment of speaking, it is not the best choice in this context because it implies that the event is already happening, rather than being imminent or about to happen.

D. is going to arrive: This option is incorrect because it uses the future continuous tense (is going to arrive) to describe a future event. While this tense is often used to describe actions that will be in progress at a specific time in the future, it is not the best choice in this context because it implies that the action (his arrival) will take some time to complete, rather than being imminent or about to happen.

The Answer is: B. arrives