The Treaty of Titalia (1817) was significant because it:

The correct answer is: a) Restored Sikkimese territory previously held by Nepal.

The Treaty of Titalia was signed on 2 December 1817 between the British East India Company and the Kingdom of Sikkim. The treaty restored Sikkimese territory that had been lost to Nepal during the Anglo-Nepalese War (1814–1816). The treaty also established a British protectorate over Sikkim.

The treaty was significant because it marked the beginning of British rule in Sikkim. The treaty also helped to secure the British position in the Himalayas.

The other options are incorrect because:

• Option b) is incorrect because the treaty did not establish a British protectorate over Sikkim.
• Option c) is incorrect because the treaty did not grant Sikkim control over Bhutan.
• Option d) is incorrect because the treaty did not abolish the Namgyal Dynasty.