Chemistry

 Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

The electrical conductivity of semiconductors is due to the presence of impurities and defects. Their conductivity increases with increase in temperature as the defects increase with the increase in temperature.

Sulphur dyes are two part developed dyes used to dye cotton with dark colours. The initial bath imparts a yellow or pale chart reuse colour. Sulphur Black 1 is the largest selling dye by volume.

Atoms of an element cannot be created, destroyed and broken into smaller parts . Dalton based this hypothesis on the law of conservation of mass and on centuries of experimental evidence.

Electrons produce fluorescence when they strike crystals, minerals and salts.

Diamagnetic materials , (e.g., TiO₂, NaCl, C₆H₆) are weakly repelled by external magnetic fields. This property is shown only by those substances which contain fully-filled orbitals i.e., no unpaired electron is present.

According to Dalton, the atoms of same element are similar in all respects. This is wrong because atoms of some elements vary in their mass and density. Such atoms of the same element having different masses are called isotopes. For example, chlorine has two isotopes having mass numbers 35 a.m.u and 37 a.m.u..

In these crystals, there is no net  dipole moment.This is because the dipoles are alternately arranged. Example: (PbZrO₃) Lead zirconate.

Weakness of intermolecular forces results in low melting temperatures of molecular solids. 

Auramine O, is a diarylmethane dye used as a fluorescent stain. In its pure form, Auramine O appears as yellow needle crystals. It is very soluble in water and soluble in ethanol.

In molecular crystals, the constituent particles are molecules. These molecules are held together by weak forces known as Van der Waal's forces. Common examples are dry ice, wax, iodine, sulphur, etc..

Solid ionic compounds cannot conduct electricity because there are no mobile ions or electrons present in the lattice. When the ionic compounds are dissolved in a liquid or molten state, they can conduct electricity with the mobile ions.

Otherwise known as quantum-induced instantaneous polarization or instantaneous dipole-induced dipole forces, the London dispersion force is caused by correlated movements of the electrons in interacting molecules. 

In the context of molecular modeling, a force field refers to the form and parameters of mathematical functions used to describe the potential energy of a system of particles (typically molecules and atoms). Force field functions and parameter sets are derived from both experimental work and high-level quantum mechanical calculations.

Dipole-dipole interactions are electrostatic interactions of permanent dipoles in molecules. These interactions tend to align the molecules to increase the attraction (reducing potential energy).

Carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) is a cell permeable dye generally used in animal cell proliferation research. 

Indian yellow, also called euxanthin or euxanthine, is a xanthonoid. It is a transparent yellow pigment used in oil paint. 

Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein.

Primuline yellow is a mixture of sodium salts and probably contains at least three thiazole rings in combination. 

Ionic compounds are generally soluble in water and other polar solvents having high dielectric constants. This is due to larger electrostatic interactions between polar solvents and ions. However, ionic compounds are insoluble in non-polar solvents.

All the above mentioned conditions favour the formation of an ionic bond .

Covalent compounds are less dense when compared to water. Very weak Van der Waal's forces hold the molecules together, hence there are large inter molecular spaces.Hence they have a low density.

Electron affinity is the amount of energy released, when an isolated gaseous atom accepts an electron to form a negative ion. Therefore, generally, the elements having higher electron affinity favour the formation of an ionic bond. 

Safranin is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring all cell nuclei red. This is the classic counterstain in a Gram stain. It can also be used for the detection of cartilage, mucin and mast cell granules.

Acridine is structurally related to anthracene with one of the central CH groups is replaced by nitrogen. Acridine, a colourless solid, was first isolated from coal tar. It is a raw material used for the production of dyes and some valuable drugs.