Explanation
According to the Search Reindexing page, search reindexing is a feature that allows you to rebuild the search index for your store or reorder portal. Search reindexing creates or updates the index of products, categories, and attributes that are searchable on your site. To rebuild the search index in the B2B Commerce app, you need to do the following steps:
Navigate to the Store record page in Salesforce.
Click on the Search tile in the Commerce app menu. Therefore, option B is correct.
Click on Rebuild Index in the Search workspace.
Confirm that you want to rebuild the index and wait for the process to complete.
Option A is false because there is no Search Reindex option in Setup, only in the Commerce app menu.
Option C is false because clicking on Community Settings will not allow you to rebuild the search index, only to configure general settings for your community, such as domain name, login options, network settings, etc.
Option D is false because there is no Search Reindexing option in the Quick Options menu, only in the Search workspace. References: Search Reindexing, Search Reindexing Overview

To replace the out-of-the-box Product Detail Card component on the product page, a developer can use three components: Product Fields Short component, Product Field Long component, and Product Detail Image Gallery component. These components are part of the standard Lightning web components that are available for B2B Commerce stores. They allow the developer to customize the product page layout and display different product fields and images3. The Product Fields Short component displays short text fields from the product object, such as name, SKU, or price4. The Product Field Long component displays long text fields from the product object, such as description or specifications5. The Product Detail Image Gallery component displays a carousel of product images from the product object or from a custom field6. The other options are not suitable for replacing the Product Detail Card component, as they serve different purposes. The Product Detail Breadcrumbs component displays the navigation path from the home page to the current product page7. The Product Detail Purchase Options component displays a button to add the product to the cart or to request a quote8. Reference: 3: Lightning Web Components for B2B Commerce - Trailhead, 4: Product Fields Short Component - Salesforce Developers, 5: Product Field Long Component - Salesforce Developers, 6: Product Detail Image Gallery Component - Salesforce Developers, 7: Product Detail Breadcrumbs Component - Salesforce Developers, 8: Product Detail Purchase Options Component - Salesforce Developers

Explanation
According to the Searchable Fields page, searchable fields are fields on the Product object that can be used as filters or facets for search results on your B2B Commerce site. Searchable fields can help users narrow down their search results and find the products that match their criteria. Three of the field types that an administrator can set as searchable fields for search are text, picklist, and picklist (multi-select). Text field type allows users to enter any alphanumeric characters as search terms. Picklist field type allows users to select one value from a predefined list of values as a search term. Picklist (multi-select) field type allows users to select multiple values from a predefined list of values as search terms. Therefore, options B, D, and E are correct. Options A and C are false because currency and checkbox are not field types that an administrator can set as searchable fields for search. Currency field type allows users to enter numeric values with decimal places and currency symbols as search terms. Checkbox field type allows users to select true or false values as search terms. References: Searchable Fields, Searchable Fields Overview

Explanation
The "Show in Menu" attribute is used to control whether a category is displayed in the navigation menu of a B2B commerce site. The navigation menu is a component that allows buyers to browse products by category.
If the "Show in Menu" attribute is set to false, the category is not shown in the navigation menu, but it can still be accessed by other means, such as search or facets. If the "Show in Menu" attribute is set to true, the category is shown in the navigation menu, unless it is hidden by other settings, such as visibility rules or active dates. References: Category Attributes; Navigation Menu Component