CSIR NET key terms

A property of cyclic, planar, conjugated systems in which delocalized pi electrons occupy a closed shell, giving unusual stability. Hückel's rule predicts aromaticity when the ring contains 4n+2 pi electrons.

One of a pair of molecules that are non-superimposable mirror images of each other. They have identical physical properties in achiral environments but rotate plane-polarized light in opposite directions.

The position of an NMR signal relative to a standard, expressed in parts per million. It reflects the local magnetic environment of a nucleus and helps identify functional groups and molecular structure.

The slowest elementary step in a reaction mechanism. It controls the overall reaction rate because the full pathway cannot proceed faster than this bottleneck.

The energy lowering gained when electrons occupy split d orbitals in a coordination complex, relative to a spherical field. It influences geometry, color, and magnetic behavior of transition-metal complexes.

The amount of strong acid or base a solution can absorb before its pH changes by a specified amount. It depends on buffer concentration and on how close pH is to the buffer's pKa.

An interaction in which electrons from a sigma bond, usually a carbon-hydrogen or carbon-carbon bond, donate into an adjacent empty or partially filled orbital, stabilizing the molecule and affecting reactivity and shape.

The ratio of a solute's concentrations in two immiscible phases at equilibrium, often octanol and water. It indicates whether a compound prefers a nonpolar or aqueous environment.

The theory that Earth's lithosphere is divided into rigid plates that move over the weaker asthenosphere. Their interactions at boundaries produce earthquakes, volcanoes, mountain belts, and ocean basins.

A state of gravitational balance in which the lithosphere floats on the denser mantle. Thicker or less dense crust stands higher, explaining why mountain roots and ocean basins maintain elevation differences.

The apparent deflection of moving objects when viewed in a rotating reference frame. On Earth, it deflects winds and currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

A large-scale ocean circulation driven by differences in water density caused by temperature and salinity. It transports heat, nutrients, and dissolved gases between ocean basins over long timescales.

A coupled ocean-atmosphere pattern in the tropical Pacific that alternates between warm El Niño and cool La Niña phases. It shifts rainfall, storms, and temperature patterns worldwide.

Periodic changes in Earth's orbit and axial orientation-eccentricity, obliquity, and precession-that alter the distribution of solar energy. They pace long-term climate fluctuations such as glacial cycles.

A sequence describing the order in which silicate minerals crystallize from cooling magma. High-temperature minerals form first, and the series helps explain mineral assemblages in igneous rocks.

A wind that results from an exact balance between the pressure-gradient force and the Coriolis force, flowing parallel to isobars. It approximates upper-air flow away from the surface and near the equator.

The principle that genetic information flows from DNA to RNA to protein in cells. DNA is replicated, transcribed into RNA, and translated into polypeptides, though exceptions such as reverse transcription exist.

Programmed cell death that removes damaged or unnecessary cells without triggering inflammation. It is essential for development, tissue homeostasis, and defense against abnormal cell growth.

A technique that repeatedly copies a specific DNA sequence using primers and a thermostable DNA polymerase. Cycles of denaturation, annealing, and extension produce exponential amplification for analysis or cloning.

An interaction in which the effect of one gene depends on or masks the effect of another gene. It can alter expected phenotypic ratios and complicates mapping of traits.

A cluster of genes transcribed together from a single promoter in prokaryotes, often regulated as a unit. It allows coordinated control of enzymes in a shared metabolic pathway.

Control of a protein's activity by binding of a molecule at a site distinct from the active site. This changes protein shape and often alters substrate affinity or catalytic rate.

A model in which allele and genotype frequencies in a population remain constant across generations under assumptions such as random mating, no selection, no mutation, no migration, and large population size.

A species whose influence on an ecosystem is disproportionately large relative to its abundance. Its removal can cause major changes in community structure and ecosystem function.

A map between two groups that preserves the group operation, so the image of a product equals the product of the images. It reveals structural similarities between groups.

A sequence whose terms become arbitrarily close to one another as the index increases. In a complete space every Cauchy sequence converges, a property central to real analysis.

A scalar for which a nonzero vector is mapped to a scalar multiple of itself by a linear transformation. Eigenvalues describe stretching, frequencies, and stability in linear systems.

A topological property meaning every open cover has a finite subcover. In Euclidean space it is equivalent to being closed and bounded, and it underlies many existence theorems.

A stochastic process in which the next state depends only on the current state, not on the full past. It is described by transition probabilities and is widely used in modeling.

A result stating that sums or averages of many independent, identically distributed random variables tend toward a normal distribution as sample size grows, regardless of the original distribution's shape.

A mathematical function that encodes the quantum state of a system. Its squared magnitude gives the probability density for finding a particle at a given position, and it evolves according to the Schrödinger equation.

A quantum principle stating that certain pairs of properties, such as position and momentum, cannot both be known with arbitrary precision simultaneously. It reflects the wave nature of matter.

The coordinate transformation between inertial frames in special relativity. It mixes space and time coordinates and explains length contraction, time dilation, and the invariance of the speed of light.

The energy level at which the probability of occupation by a fermion is one-half at nonzero temperature. At absolute zero it separates filled from empty states in a fermion system.

A statistical-mechanics ensemble representing a system in thermal contact with a heat bath at fixed temperature, volume, and particle number. Its probabilities are weighted by the Boltzmann factor.

The energy difference between the top of a material's valence band and the bottom of its conduction band. It determines whether a solid behaves as a conductor, semiconductor, or insulator.