Select the most appropriate adjective to fill in the blank. Tejasswini was…

An adjective fill-in-the-blank question is answered by matching the word to both the meaning the sentence implies and the idiomatic pattern of the words around the blank — especially the preposition that immediately follows it. Participial adjectives formed from verbs (ending in "-ed", such as "surprised", "annoyed", or "excited") describe a person's emotional reaction, and they combine naturally with "by + cause" to name what triggered that reaction.

Here, the blank is immediately followed by "by the unexpected guest" — the cause of Tejasswini's reaction. An unannounced visitor arriving is a classic trigger for astonishment. "Surprised" names exactly that reaction, and "surprised by" is the standard idiom for saying an unforeseen event caused someone's astonishment — matching both the meaning and the grammar of the sentence.

Checking the remaining options against the same sentence confirms none of them fit:

• "Shy" describes a lasting personality trait of being reserved around people in general, not a one-time reaction to a guest's unannounced arrival.

• "Tough" describes physical or mental resilience, or how difficult a task or situation is, not a person's emotional response to being caught off guard by a visitor.

• "Uncertain" describes doubt about a fact or a decision, not the astonishment caused by someone unexpectedly turning up.

So the adjective that correctly completes the sentence is "surprised."