**21. Explain different forms of Boolean expression?**

There are two forms of Boolean expression

Sum of products (SOP) form.

The Product of sum (POS) form.

**22. Explain a Logic gate ?**

A logic gate is an idealized or physical electronic device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device. Most logic gates take an input of two binary values, and output a single value of a 1 or 0.

**23. What is Pair, Quad, and Octet in karnaugh map ?**

Two adjacent cell of Karnaugh map is called as Pair. It cancels one variable in a K-Map simplification.

A Pair of four adjacent pairs in a Karnaugh map is called a quad. It cancels two variables in a K-Map simplification.

A Pair of eight adjacent pair in a karnaugh map is called an octet. It cancels four variables in a K-map simplification.

**24. What is a Combinational logic ?**

Combinational logic is a type of digital logic which is implemented by Boolean circuits, where the output is a pure function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the history of the input.

**25. What is Hexadecimal Number System ?**

The hexadecimal numeral system, is a numeral system made up of 16 symbols (base 16). The standard numeral system is called decimal (base 10) and uses ten symbols: 0,1,2,3,4,5,6,7,8,9. Hexadecimal uses the decimal numbers and six extra symbols. The hexadecimal system is commonly used by programmers to describe locations in memory because it can represent every byte as two consecutive hexadecimal digits instead of the eight digits that would be required by binary.