What is the sharpest Nikon F-mount prime lens you can get? Sorry if this is a really basic question but I just started getting into photography and I'm so confused by all the numbers. My uncle gave me a D750 and I want to take really clear photos of my cat and some local flowers here in Oregon but my current lens makes everything look kinda fuzzy.

I have about $350 or maybe $400 to spend if I save up for another month. I heard primes are the way to go for sharpness but there are so many options out there I have no idea where to start... do I need a specific brand or does Nikon make the best ones?