Step 1: Understanding the Concept:
Assertion (A) pertains to the specific literary work and meter of Banabhatta.
Reason (R) pertains to the authorship of a devotional stotra.
Step 3: Detailed Explanation:
Statement (A) is true.
'Chandishatakam' is a collection of 102 verses composed by Banabhatta (the author of Kadambari).
He wrote it to praise Goddess Chandi after his relative Mayurabhatta composed 'Suryashatakam'.
The entire work is indeed composed in the Sragdhara meter (a 21-syllable meter suitable for grand, fierce descriptions).
Statement (R) is also true.
The 'Tripurasundari Stotram' (beginning with "Kadamba-vana-charinim...") is a popular devotional hymn attributed to Adi Shankaracharya.
It is part of the vast corpus of Stotra literature he is credited with.
However, (R) has no logical connection to (A).
The fact that Shankaracharya wrote Tripurasundari Stotram does not provide the reason why Banabhatta wrote Chandishatakam in the Sragdhara meter.
These are two independent facts about Sanskrit literature.
Step 4: Final Answer:
Both statements are correct, but (R) is not the correct explanation for (A). Therefore, Option (B) is correct.