Answer
Yes, Inserts a 'comment' which will not display on the browser screen, but can be viewed in html file itself when you inspect its source using <!-- -->

Answer

• UL: Unordered and Bullet List. Items in the list are LI elements. Lists can be nested. 
  
• OL Ordered List Numberd (or lettered) list. Items in the list are LI elements. Lists can be nested.
  
• LI List item An item in a bullet or numbered list. List items can include other lists (nesting lists), line breaks, and other HTML tags. Close tags are optional.  
  
• DL Descriptive List or Definition List A list of terms with definitions or entries with annotations. Contains DT and DD elements. 
  
• DT elements are the 'terms' or main entries while DD elements are the definitions or annotations. 
  
• DT Term in Definiton list In an annotated list, the item or term being annotated. 
  
• DD Definition in Definition list In an annotated list, the annotation or definition.
  

Answer

1. EM Tag: Derived from emphasis tag. Used for important text and generally displays as Italic. 
   
2. STRONG Tag: Strong emphasis for very important text. Generally displays as Bold. 
   
3. CITE Tag: Citation, Title of a cited work. Generally displays as Italic. 
   
4. B Tag: Bold tag. Displays text as bold. 
   
5. I Tag: Italic tag, displays text as italic. 
   
6. U Tag: Underline tag, Shows text as underlined.
   

Answer
No, Although they will works in all browsers, because the closing tag is considered optional. But never rely on this. It might produce unexpected results and/or errors if you forget the end tag.

Answer
The elements with no content are empty elements. They do not have any end tag, for example < br > element used for line break.

Answer
Html tags are keywords(tag name) surrounded by angle brackets.

• Html tags comes in pairs
• The first tag in pair is the start tags,the second tag is end tag.
• End tag is written like a start tag, but with slash before Tag name.