Question:What are the general language features of php? 

Practicality: It requires minimum  knowledge of programming.Power: It has the ability to interface with databases, form and create pages dynamically.Possibility: Developers are rarely bound to any single implementation solution.Price: It is open source software.

Question:What are the encryption techniques in PHP? 

PHP implements the MD5 hash algorithm using the md5() function,
eg : $encrypted_text = md5 ('password');

Question:What is the use of "enctype" attribute in a html form? 

The enctype attribute determines how the form-data should be encoded when submitting it to the server. We need to set enctype as "multipart/form-data" when we are using a form for uploading files

Question:Which functions are used to add file in a script? 

Thare are two functions are used to add file in a script
1.The include()function
2.The require() function

Question:
What are passing arguments by reference and passing arguments by value?
 

passing arguments by value:Means any changes made to those values within the scope of the function are ignored outside of the function.
passing arguments by reference:Means any changes made to those values within the scope of the function are reflected outside of the function.

Question:What is the difference between Session and Cookie? 

The main difference between sessions and cookies is that sessions are stored on the server, and cookies are stored on the user’s computers in the text file format. Cookies can not hold multiple variables,But Session can hold multiple variables.We can set expiry for a cookie,The session only remains active as long as the browser is open.Users do not have access to the data you stored in Session,Since it is stored in the server.Session is mainly used for login/logout purpose while cookies using for user activity tracking

Question:What are the types of key of array? 

There are two types of key of array. It can be numerical And associative.
Numerical :It stores each array element with numeric index name.
associative : It contains characteristic element or string index name.

Question:
What are class and object?
 

Class:Classes are intended to represent those real-life items that coder like to manipulate within an application.
object: An instance of class is called object.

Question:What is property overloading? 

Property overloading continues to protect properties by forcing access and manipulation through public methods, yet allowing the data to be accessed as if it were a public property.

Question:What should we do to be able to export data into an Excel file? 

The most common and used way is to get data into a format supported by Excel. For example, it is possible to write a .csv file, to choose for example comma as separator between fields and then to open the file with Excel.