Direct dyes:
These dyes have high affinity for cotton, rayon and other cellulose fibre. So they are applied directly as they fix firmly on the fabric.
Eg: Congo red
Indirect dyes:
These dyes have a poor affinity for cotton fabrics and hence do not dye directly. They require pretreatment of the fibre with a mordant. 
Eg: Alizarin

The diet that contain body building, energy giving, protective foods in right proportion for the smooth functioning of the body is called as balanced diet.

1. It should have suitable colour.
2. It should be able to fix itself or be capable of being fixed to the fabric.
3. It should be fast to light.
4. It should be resistant to the action of water, dilute acids and alkalies.

i) Drugs that are used in the treatment and cure of any specific disease.
ii) Drugs that have some characteristic effect on the animal organism. But do not have any remedial effect for a particular disease. This class includes Morphine, Cocaine etc.,

It is a substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefits of the recipient.

1. The person being tested blows through a tube which bubbles the breath through a solution of chemicals containing sulfuric acid, potassium dichromate, water and silver nitrate .
2. Oxidation of the alcohol results in the reduction of dichromate to chromic ion, with a corresponding change in colour from orange to green .
3. An electrical device employing a photocell compares the colour of the test solution with a standard solution, giving a quantitative determination of the alcohol content.
4. The test provides a quick and reproducible determination of the amount of alcohol in a person's breath and is a numerical measure of the amount of alcohol in the blood stream.

i) Radiocarbon dating:
It is a method by which the age of fossil wood or animal is determined using C-14 isotope.
ii) Study of chemical reactions:
1. The nature of some of the chemical reactions can be studied by mixing it with a radioisotope with non-radioactive isotope of the reactants .
2. The radioisotope used for this purpose is called as radiotracer.
3. For example, By photosynthesis plants synthesize carbohydrate from carbon dioxide and water as shown in the following reaction.
\(\underset { Carbon\quad di\quad oxode }{ 6C{ O }_{ 2 } } +\underset { Water }{ 6{ H }_{ 2 } } O\overset { Light }{ \longrightarrow } \underset { Sugar }{ { C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 } } +\underset { Oxygen }{ 6{ O }_{ 2 } } \)
4. To find whether the oxygen evolved in this process comes from CO₂ or H₂O by using radioisotope 0-18 as tracer, it was found that evolved oxygen comes from H₂O
Diagnosis:
Radioisotopes are found very useful to diagnose and understand many diseases.
Ex: Iodine - 131 :- Location and detection of brain tumour, Thyroid gland disorder.
Radiotherapy:
Radioactive isotope are used in the treatment of many diseases. This kind of treatment is called radiotherapy.
Ex: Cobalt 60 :- cancer.

1. Nano particles are unstable when they contact with oxygen .
2. Their exothermic combustion with oxygen can easily cause explosion .
3. Because nanoparticles are highly reactive, they inherently interact with impurities as well.
4. Nanoparticles are usually considered biologically harmful and toxic .
5. It is difficult to synthesis, isolate and apply them .
6. There are no hard-and-fast safe disposal policies for nanomaterials.

1. It should not be toxic.
2. It should not cause any side effects .
3. It should not affect the receptor tissues .
4. It should not affect the normal physiological activities .
5. It should be effective in its action .
6. Chemicals which satisfy the above criteria only are preferred as drugs.