Explanation
To create a chart in Oracle APEX, you need to provide some required fields that define the data source and appearance of the chart. You can use either the Create Page Wizard or Page Designer to create a chart. The required fields for creating a chart are:
Data Source: This field specifies the SQL query that returns the data for the chart. The query must include at least one column for the label and one column for the value of each data point. You can also include additional columns for grouping, color, or tooltip information.
Value Column: This field specifies the column from the data source query that contains the numeric values for the chart. The values are used to plot the data points on the chart and determine the size of each data point or segment.
Name: This field specifies the name of the chart region. The name is used to identify the region in Page Designer and other components, such as dynamic actions or processes.
Label Column: This field specifies the column from the data source query that contains the labels for the chart. The labels are used to display the name of each data point or segment on the chart or in the legend.

Explanation
A validation is a rule that checks the data entered by end users before processing it. A validation of type Item is numeric checks if a page item value is a valid number. When the page is submitted, if the validation fails, an error message is displayed both in the notification area (atthe top of the page) and below the item (next to the item label). To cause the validation error to appear only in the notification area, you need to remove P1_SALARY from the validation Associated Item attribute. The Associated Item attribute specifies which page item is associated with the validation and where to display the error message if the validation fails.
Setting the value Required to Yes on P1_SALARY or setting Display Location to Inline in Notification will not affect the validation error display. Verified References: [Creating Validations - Oracle Help Center],
[Validation Attributes - Oracle Help Center]

Explanation
A smart filters page is a type of component that features a single search field at the top of the page and a search results report (classic report, cards, map, or calendar) at the bottom. A smart filters page behaves similarly to faceted search, but it features a more space efficient layout. Two of the features of a smart filters page are:
Consists of a single search field with filters at the top of the page and a report at the bottom. This feature provides a simple and compact user interface that allows users to enter text in the search field and see suggested filters based on their input. Users can also see and modify applied filters at any time.
Each filter displays as a suggestion chip with a single count of how often the specific suggestion value occurs. This feature provides useful information to users about how many records match each filter value. Users can also choose between different types of suggestions, such as dynamic, static, or SQL query.

Explanation
The commission yn column will restrict acceptable values to TRUE or FALSE because of the /check modifier in the column name. This modifier adds a check constraint to the column based on the values specified after it.
The yn suffix indicates that the column is of type VARCHAR2(1). The other options are incorrect because they do not reflect the effect of the /check modifier or the yn suffix. Verified References: Using Quick SQLAbout Quick SQL Shorthand Syntax

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.