Harshacharita book was written by which of the following writers?

The correct answer is Banabhatta.

The Harshacharita (meaning "Deeds of Harsha") is one of the most celebrated works of classical Sanskrit literature, and it was composed by the renowned Sanskrit prose writer Banabhatta.

Let us understand this step by step:

Step 1 – Who was Banabhatta?
Banabhatta (also written as Bāṇabhaṭṭa) was a 7th-century CE Sanskrit scholar and poet who served as the court poet (Asthana Kavi) of the great Indian emperor Harshavardhana (also known as King Harsha), who ruled the Vardhana dynasty from approximately 606 CE to 647 CE.

Step 2 – What is the Harshacharita?
The Harshacharita is a biographical prose work written in ornate (Champu-style) Sanskrit. It chronicles the life and achievements of Emperor Harshavardhana, beginning with Banabhatta's own autobiography and then narrating Harsha's rise to power, his valor, and his administration. It is considered one of the earliest examples of historical biography in Sanskrit literature.

Step 3 – Eliminating the other options:
Harisena – was a court poet of the Gupta emperor Samudragupta, famous for composing the Allahabad Prashasti (eulogy inscribed on the Allahabad Pillar). He did NOT write the Harshacharita.

Amarasimha – was a Sanskrit grammarian and lexicographer, best known for compiling the Amarakosha, a Sanskrit thesaurus. He had no association with the Harshacharita.

Vararuchi – is traditionally associated with Sanskrit grammar (linked to the Prakrit grammar text Prakrit Prakasha) and is considered one of the Navaratnas of the Vikramaditya court. He also did NOT write the Harshacharita.

Step 4 – Conclusion:
Only Banabhatta is correctly associated with the Harshacharita. Apart from this work, Banabhatta also authored the famous Sanskrit novel Kadambari, which is considered a masterpiece of classical Sanskrit prose fiction. His literary genius earned him the title "Vachaspati" (Lord of Speech).

Therefore, the Harshacharita was written by Banabhatta.