1. Which of the following tags is not a valid way to begin and end a PHP code block? 1. <% %> 2. <? ?> 3. <?= ?> 4. <! !> 5. <?php ?>

The only valid PHP tags from those are <?php ?> & <? ?> According to PHP manual, When PHP parses a file, it looks for opening and closing tags, which are <?php and ?> which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser. PHP also allows for short tags <? and ?> (which are discouraged because they are only available if enabled with short_open_tag configuration file directive, or if PHP was configured with the --enable-short-tags option. If a file is pure PHP code, it is preferable to omit the PHP closing tag at the end of the file. This prevents accidental whitespace or new lines being added after the PHP closing tag, which may cause unwanted effects because PHP will start output buffering when there is no intention from the programmer to send any output at that point in the script

Only <! !> is not valid. <% %> are valid if asp_tags are enabled in <? ?> are valid if short_tags are enabled in <?= ?> are valid and is a shorthand for <?php echo ?> (and it's also a part of the PSR-1 PHP coding standard) And, of course, <?php ?> are the default valid tag.

The only invalid tags are <! !>.

 

All others are valid (with short_open_tag and asp_tags php directives set to on)

not valid tags:1.<% %>   3.<?= ?>  4.<! !>

valid tags:3.<? ?>  5.<?php ?>