Questions

Adders are generally of five types:

1.Ripple Carry Adder:

The Ripple carry adder(RCA) consists of a building block named Half Adder(HA) which is cascaded to form a Full Adder(FA). These buildingblocks HAs and FAs are also the building blocks of all types of adders.The n full adders are cascaded to form n bit RCA.

The full adder has three input pins(input Ai,input Bi,carryin Ci) and two output pins(Sum and Ci+1).Its equations are:

Sum=Ai^Bi^Ci

Ci+1=Ai.Bi+Bi.Ci+Ai.Ci

2. Carry Lookahead Adder:

The Carry Lookahead Adder(CLA) reduces the delay as that in RCA. Let Gi=Ai.Bi, and Pi=Ai^Bi, then Ci+1=Gi+Pi.Ci.

The expressions for Sum and Ci+1 is then defined completely in terms of input pins rather wait for input carry to appear.

3. Carry Select Adder:

The carry select adder uses duplicate modules for each combination of input carry(i.e. 1 and 0).The multiplexers then select the appropriate sum and carry output according to the carry output of the preceding stages.

4. Carry Skip Adder:

The carry skip adder are as fast as carry lookahead adders which are the fastest adders but its spped decreases to about 20-30% if input operands are 64-bit or more. In these adders we divide the input bit stream into various blocks and make use of two observations:

-if each element of the two bit streams are unequal,i.e. Ai!=Bi than the carry input of the block is equal to the carry input.

-if each element of the two bit streams are equal,i.e. Ai=Bi than the carry input of the block is opposite of the carry input.

5. Carry Save Adder:

The carry save adder reduces the addition of three elements into addition of two elements,i.e. if you want sum of nine numbers it reduces it into sum of six numbers. In first step the sum of three numbers is calculated without bothering for the carry.During the second step only carry is calculated which is then added to the generated sum to give the required sum. 

Electronegativity refers to the ability of an atom to attract shared electrons in a covalent bond. The higher the value of the electronegativity, the more strongly that element attracts the shared electrons.

Electronegativity increases from bottom to top in groups, and increases from left to right across periods. Thus, fluorine is the most electronegative element and lithium is the least.

Simple covalent compounds are generally named by using prefixes metal name + nonmetal name + suffix –ide to indicate how many atoms of each element are shown in the formula. Also, the ending of the last (most negative) element is changed to -ide. The prefixes used are mono-, di-, tri-, tetra-, penta-, hexa-, and so forth.

Carbon monoxide is a common atmospheric pollutant in the world which is produced in combustion process in automobiles and industries. It has no smell and cannot be seen.

A 40% solution of Formaldehyde known as Formalin is used in the preservation of biological specimens because of its hardening action on proteins.