Form 1120 is a crucial tax document utilized by corporations in the United States to disclose their income, gains, losses, deductions, and credits for federal income tax goals. In Delaware, corporations are expected to submit Form 1120 if they are operating within the state or have obtained income from sources within its boundaries.

A Delaware C Corporation (C Corp) is a type of business entity formed under the laws of Delaware and is taxed separately from its owners. A C Corp is considered a separate legal entity from its shareholders, meaning it can enter into contracts, own assets, and conduct business in its name.

C corporations conducting business in Delaware must pay an annual fee known as the Delaware state franchise tax, a privilege fee for operating within the state's jurisdiction.

C corporations use Form 926 to report property transfers to foreign corporations.

Regardless of taxable income, every US-based domestic corporation must file tax Form 1120. 

The following entities fall under the obligation to file tax Form 1120:

1. Businesses opting for corporate taxation. These businesses must also complete Form 8832 and include a copy of Form 1120.
2. Limited liability companies (LLCs). LLCs file Form 1120 only if they've chosen corporate taxation. Partnership LLCs use Form 1065, while single-member LLCs typically file taxes through the owner's personal federal tax return.
3. Farming corporations. They are required to file Form 1120 to report their income/losses.
4. Corporations with an ownership interest in a FASIT (Financial Asset Securitization Investment Trust).
5. Foreign-owned domestic disregarded entities. If a foreign entity owns 100 percent of a domestic disregarded entity (D.E.), the D.E. is treated as separate from its foreign owner. The foreign entity must file Form 1120 and attach Form 5472.

Additionally, some types of corporations may need to complete additional forms, such as Form 1120 (Schedule N), for foreign operations in the U.S. Small corporations might not be required to fill out these additional forms. You can locate them by searching for "Form 1120" using the IRS Forms and Publications tool.

Individuals employ Form 1040 to file personal income taxes, whereas C corporations utilise Form 1120 for corporate tax returns. The primary distinction lies in the taxpayer type: 1040 is for individuals, and 1120 is for corporations.

The IRS grants tax-exempt status to specific organisations, such as:

1. Charitable organisations
2. Social welfare organisations
3. Social clubs
4. Trade associations
5. Labor organisations
6. Veterans' organisations
7. Political organisations

The IRS maintains a comprehensive list of tax-exempt organisations, available here. These organisations are required to submit an information return, which may include Form 990, Form 990-EZ, and Form 990-PF.

In such cases, you need to rectify the mistake by amending the form. Utilise Form 1120X, the Amended U.S. Corporation Income Tax Return, for this purpose. Form 1120X must be submitted within three years from the original return.

To complete Form 1120X, you'll need the following information:

1. Business name
2. Explanation of changes
3. Business address
4. Details on payments and credits
5. Data on income and deductions
6. Tax amount due or overpayment
7. Employer Identification Number (EIN)
8. Signature