Attibutes names and their values are case-sensitive or not?

Yes,Attributes and their values are case-sensitive. Both should be write on lowercase letters.In new versions of HTML W3C(World Wide Web Consortium) strongly said to use lowercase letters.Like: HTML 4

Can we write a comment into the HTML?

Yes,HTML provide us facility to write comments on HTML file.Comments that we write on HTML file are ignored by the browser so it will not display on browser.
Syntax:
<!-- Here write your comment -->

<!--      --!>

Choose correct syntax as per w3c standard:

1.<br><p>Welcome to r4r</br></p>
2.<p>Welcome to r4r</p>
3.<br><p>Welcome to r4r</p></br>
4.<b><p>Welcome to r4r</p></b>
5.<b><p>Welcome to r4r</b></p>

Choose correct syntax as per w3c standard:
2.<p>Welcome to r4r</p>
4.<b><p>Welcome to r4r</p></b>

Choose correct syntax for making a submit button:
1. <form action=””>
      <input type="submit" name="s1" value=" Press " />
   </form>
2.
      <input type="submit" name="s1" value=" Press " />
3. <form action=””>
  
   </form>
4. <form action=””>
      <input type="button" name="s1" value=" Submit " />
   </form>

1. <form action=””>
      <input type="submit" name="s1" value=" Press " />
   </form>

4

4

Choose correct syntax used for external CSS
1.<style type="text/css">
body {background-color: red}
</style>
2.<link rel="stylesheet" type="text/css" href="r4rcss.css">
  Here r4rcc.css is in to same directory .
3. Both
4. None

2.<link rel="stylesheet" type="text/css" href="r4rcss.css">  Here r4rcc.css is in to same directory

Choose correct tag to break line in XHTML?
a. <br>
b. <br />

b. <br /> 
                 

Choose true option :

1.HTML allow images and objects to be embedded on web page to create interactive forms by using some script.
2.HTML allow images and objects to be embedded on web page to create interactive forms by using tags.
3.Both of the above
4.None

2.HTML allow images and objects to be embedded on web page to create interactive forms by using tags

DHTML stands for
a. Direct Hyper Text Markup Language
b. Dual Hyper Text Markup Language
c. Dynamic Hyper Text Markup Language
d. Domain Hyper Text Markup Language

c. Dynamic Hyper Text Markup Language

c

DOM is an 
a. Microsoft Standard
b. Sun Microsystem Standard
c. W3C standard

c. W3C standard

Give an example shows properly nested element in XHTML?

 In HTML we can improperly nested some element each other like that,
<b><i>Gives text as bold and italic</b></i>
 Where as In XHTML, all elements must be properly nested within each other like that,