I need to ask that what is string in PHP. Is it an array in PHP or not. Please give true justifications.
In PHP, a string is a primitive type, meaning it's not an array. See here for the other primitive types supported by PHP.
You can read the documentation about php strings at
A string in PHP is essentially a byte array (but not in the sense of a PHP's "array"); i.e., it's a buffer with only one piece of meta-data -- the size of the buffer.
An array in PHP is a double-linked hash table map, where the keys can be integers, strings, or a mixture of both.
In terms of PHP's type system, strings and arrays are two of the basic types.