is it correct to write <hr width="50px" align="center" /> ?

Answer 1

Yes. It would give you a horizontal line that would be 50 pixels long and be aligned to the center of the page.

Answer 2

correctly

Answer 3

HTML <hr> Tag
Differences Between HTML 4.01 and HTML5
In HTML5, the <hr> tag defines a thematic break.

In HTML 4.01, the <hr> tag represents a horizontal rule.

However, the <hr> tag may still be displayed as a horizontal rule in visual browsers, but is now defined in semantic terms, rather than presentational terms.

All the attributes are removed in HTML5. Use CSS instead.

Source: http://www.w3schools.com/tags/tag_hr.asp

Answer 4

yes

Answer 5

да

Answer 6

No, it's wrong, according to w3schools, br tag supports global attributes only..
Source: http://www.w3schools.com/tags/tag_br.asp

Answer 7

no ! :-)))))
This tag is to place a breakline which doesn't have any kind of measurememt...