Explanation
You can create a report with form in Oracle APEX by using either the Create Application Wizard or the Create Page Wizard. The report can be either an interactive report or a classic report, and the form can be either a single row form or a multi row form. The report with form combination enables you to view and edit data from a table or a query in a single page. You can also customize the report and form attributes, such as the columns, regions, buttons, validations, processes, and so on. Verified References: [Creating a Report Using the Create Page Wizard - Oracle], [Creating a Report with Form on Table - Oracle]

Explanation
A Link Column is a special column type that you can define for an interactive report to create a link to another page, URL, or custom target. A Link Column is always displayed as the first column in the report, regardless of the order of the columns in the query. A Link Column cannot be sorted, hidden, or moved by an end user using the Actions menu or the column header. However, a developer can change the position and visibility of a Link Column by editing the report attributes in Page Designer.

Explanation
Collections are temporary tables that store session-specific data in memory. They can be used for various purposes in APEX applications. Some uses of collections are:
You insert, update, and delete collection information using PL/SQL API APEX_COLLECTION. This API provides several procedures and functions to manipulate collections and their members.
Use collections to temporarily capture one or more nonscalar values. For example, you can use collections to store the results of a query, the values of page items, or the selections of a report.
Collections can be accessed, manipulated, or processed during a user's specific session. For example, you can use collections to pass data between pages, perform calculations on collection members, or create reports based on collections.
Collections do not enable you to store rows and columns in the current session into database tables.
Collections are stored in memory and are not persistent across sessions.

Explanation
To reposition the page items and display P21_UNIT_PRICE next to P21_PRODUCT_NAME, you can use either of these methods:
In Page Designer, use the Middle Pane, click P21_UNIT_PRICE and drag the item until it is directly next to P21_PRODUCT_NAME. This method allows you to visually arrange the items on the page layout.
In Page Designer, select P21_UNIT_PRICE and then in the Property Editor, under Layout set Start New Row to Yes. This method changes the attribute of the item to start a new row in the grid layout. The other options, A and D, are incorrect because they would not achieve the desired result. Setting Start New Row to Yes for P21_PRODUCT_NAME would move it to a new row, not next to P21_UNIT_PRICE. Right-clicking P21_UNIT_PRICE and selecting Start New Row would not change the attribute of the item, but only move it to a new position in the Layout tab. Verified References: Positioning Page ItemsLayout Tab