Final answer:
Indifference is not a category of prayer as it suggests a lack of interest, unlike intercession, thanksgiving, and meditation which are active forms of prayer.
Step-by-step explanation:
The question asks which of the following is not a category of prayer. The categories of prayer typically include forms like Intercession (praying on behalf of others), Thanksgiving (expressing gratitude), and Meditation (reflective prayer or contemplation seeking a deeper communion with the divine). Indifference does not fall into the category of prayers because it denotes a lack of concern or interest, which is contrary to the essence and intention behind prayer, which is active communication or an appeal to a higher power in some form.