iPad displays liquid detection alert and has charging issues, WILL THE WARRANTY COVER IT?

Given your description, the charging cable itself may be the source of the problem. As a first step, exchange the charging cable with a certified replacement - preferably of Apple origin. If the problem clears, as is perhaps likely, discard the original cable.

As your iPad is not designed to be water resistant, your iPad warranty does not cover water damage or any consequences thereof. iPads reportedly have hidden Liquid Contact Indicators (LCIs) that will provide evidence of exposure to moisture - this providing evidence that can be used to deny warranty coverage. That said, a technical fault that misreports moisture detection would be covered by the one-year limited warranty.

If you have benefit of an active AppleCare+ plan, your iPad will be covered for accidental and water damage - and any costs associated with repairs or replacement would be reduced to a small excess/deductible fee.

For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange a qualifying iPad for a renewed/refurbished device of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair while expensive will be somewhat less than the cost of a replacement iPad.

As for out-of-warranty repair costs, Apple offers a fixed-price price repair. You can verify eligibility and cost for your region/country here:

iPad Repair & Service - Apple Support

If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.

I wasn't referring the Power Adapter (often incorrectly referred to as the "charger"), but explicitly the USB charging cable with which you connect the Power Adapter to your iPad's USB-C charging connector.

While substituting the Power Adapter is also a useful diagnostic exercise, you should change the cable.

I went to Mobile Care, an Apple-authorized store, and they said that my charging port has green corrosion due to the humidity in the air over the past few months. They are suggesting a unit replacement because, according to them, they do not offer repairs, and they are asking me to pay the full price for a replacement. I do not have that kind of money because I am only a college student.

How can I fix the green corrosion myself, or can I have a third-party technician repair my device? I badly need this iPad for my university studies.

I have tried using other chargers, like charger from my iPhone, the iPad still not charging.