1. DOS is not an example of a mobile operating system.

2. Android Android (Android Droid) and Apple iOS (Apple iOS) is a mobile operating system.

3. Mobile operating systems are operating systems that run on mobile devices such as smartphones, tablets, and smartwatches.

In Microsoft Word 2019, you can add page numbers to your document by using the "Insert" tab. The "Insert" tab contains various options, including the "Page Number" option, which allows you to insert page numbers at different locations in your document.

Integrated circuits (ICs) were first introduced during the third generation of computers. The third generation of computers, which emerged in the 1960s, saw the development and widespread use of integrated circuits. These tiny electronic circuits contained multiple transistors, resistors, and capacitors on a single semiconductor chip. The use of integrated circuits significantly reduced the size of computers, increased their processing speed, and improved their reliability, marking a significant advancement in computer technology.