### What are the three types of transmission modes?

Based on the direction of data from sender to receiver, there can be 3 types of transmission modes which are discussed below.

### What are the disadvantages of E-commerce?

Despite of the many advantages of E-commerce, there are some disadvantages of E-commerce. These disadvantages are minor and most of them will be no more with time and updates in technology. However, following are some of the disadvantages of E-commerce.

### What are the three criteria necessary for an effective and efficient network?

A network must meet a certain number of criteria to become useable in real world situation. Most important of these criteria are the three criteria as follows.

### What are the fundamental characteristics for the effectiveness of a data communications system?

The effectiveness of a data communications system depends on the following four fundamental characteristics.

### Data Communications:

Data communications are the exchange of data between two devices using one or multiple forms of transmission medium. The devices are in need to be a part of a communication system made up of hardware and software.

Following are the five components of a data communications system.

### Molarity (M):

Molarity is defined as the number of moles of solute per litter of solution. That is,

Here,
W = weight of solute.
M = molecular mass of solute
V = volume of solution

### Show that the half-life of a second order reaction is inversely proportional to its initial concentration.

For the simple second order reaction 2A→product, we know the rate constant is given by,

For half life,  and

Hence,

as k is a constant,

### Derive an expression for the rate constant of 2nd reaction of the type, 2A→product.

2A → Product
initial concentration : a molL-1                       →                              0
final concentration (t=t) : (a-x) molL-1             →                  x molL-1

Integrating,

### Derive an expression for the rate constant of a first order reaction. Give its units.

Let us consider a first order reaction,

A → product

Suppose at the beginning of the reaction, that is, when t=0, the concentration of A is amolL and when t=t, the concentration of A is (a-x)molL.

For a first order reaction, the rate of reaction,

where k is the rate constant.

integrating,

Here, c is the constant of integration.

### Order:

Order of a reaction is defined by the number of atoms or molecules, whose concentration change during the reaction and determine the rate of the reaction.

For example,

It is a first order reaction.

It is a second order reaction.