Practice MCQ Questions and answers on Chemistry-GK

Pencils create marks via physical abrasion, leaving behind a trail of solid core material that adheres to a sheet of paper or other surface. They are noticeably distinct from pens, which dispense liquid or gel ink that stain the light colour of the paper. Most pencil cores are made of graphite mixed with a clay binder, leaving grey or black marks that can be easily erased. Graphite pencils are used for both writing and drawing, and the result is durable: although writing can usually be removed with an eraser, it is resistant to moisture, most chemicals, ultraviolet radiation and natural aging. Other types of pencil core are less widely used. Charcoal pencils are mainly used by artists for drawing and sketching.

To separate a mixture of alcohol (ethanol) and water, you can use a process known as fractional distillation. This technique relies on the fact that the compounds in the mixture have different boiling points. Since ethanol boils at a lower temperature (78.5 degrees Celsius) than water, the alcohol vaporizes while most of the water remains a liquid.

The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively. All heavier elements, called metals in astronomy, account for less than 2% of the mass. The Sun inherited its chemical composition from the interstellar medium out of which it formed: the hydrogen and helium in the Sun were produced by Big Bang nucleosynthesis.

In sequential order, Hydrogen, Oxygen, Carbon and Nitrogen are the most abundant elements by number in the living system. Hydrogen constitutes 49.8% of living systems, while Oxygen constitutes 24.9%; Carbon and Nitrogen account for 24.9% and 0.27% respectively. It is not surprising, therefore, that the living cell is between 60% and 90% water.

Photovoltaics (PV) use silicon solar cells to convert the energy of sunlight into electricity. Operates under the photoelectric effect which results in the emission of electrons.

Oxygen is the most abundant element in the earth’s crust, comprising 46.6% or the crust by weight. Silicon 28%, aluminum 8.2%, iron 5.6%, calcium 4.2%, sodium 2.5%, magnesium 2.4%, potassium, 2.0%, and titanium 0.61% also comprise the crust. Given the abundance of oxygen and silicon, the silicates are the most abundant minerals in the earth’s crust.

Titanium metal is important for its strength, low density and corrosion resistance. It has bitter corrosion resistance and less reactivity than aluminium. Hence, Titanium pins remains uncorroded in the body.

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. Semiconductor material (date first used): the metalloids germanium (1947) and silicon (1954) — in amorphous, polycrystalline and mono-crystalline form; the compounds gallium arsenide (1966) and silicon carbide (1997), the alloy silicon-germanium (1989), the allotrope of carbon graphene (research ongoing since 2004), etc.

The heaviest naturally stable element is uranium, but over the years physicists have used accelerators to synthesize larger, heavier elements.

According to the reactivity series , elements which are above of hydrogen can replace hydrogen. Hence Sodium will replace hydrogen from acids to form salts.