Fill in the blank with the most appropriate word form from the given…

The correct answer is Option (3) → miss

Simple present for a habit:

• The simple present describes something that happens again and again.
• Whenever means "every time that", so the clause after it describes a repeated event and takes the same tense as the main verb.
• Clue word: "whenever". The main verb "look" is in the simple present, so the blank is miss.
• Complete sentence: My pet dog died five years ago. I look at our old pictures whenever I miss him.
  Example: I call my mother whenever I feel lonely.

Why the Other Options are Incorrect?

Option 1: am missing — Incorrect. The present continuous describes something going on at this moment, not a repeated habit.
Example: I am missing my friends today.

Option 2: missed — Incorrect. The simple past describes a finished event and clashes with the present habit "I look".
Example: I missed the bus yesterday.

Option 4: had missed — Incorrect. The past perfect is used for an action before another past action; the sentence is about the present.
Example: The train had left before we reached the station.

Contrast: "whenever" marks a repeated habit, so it takes the simple present miss; the present continuous "am missing" describes only this moment.