General Science Chemistry MCQ

[B] 2

Notes:

Valency is number of electrons gain or loss to achieve noble gas configuration I.e. fully filled octet. Magnesium (Atomic number = 12) has electronic configuration 2, 8, 2. Since magnesium has 2 electrons in its outermost shell, hence it’s valency is 2, i.e., it will lose it’s 2 electrons to achieve noble gas configuration (2,8).

[C] Carbon dioxide

Notes:

Global Warming refers to average increase in the earth’s temperature due to increase in air pollution by green house gases. The greenhouse gases such as carbon dioxide and methane accumulate into the atmosphere and trap heat that would otherwise normally escape into the outer space.

[C] Nickel

Notes:

Alloys of aluminum being light, having high melting point and resistant to corrosion are used in making aircraft. The alloys used are magnalium and duralumin.

[A] Silicon carbide

Notes:

Silicon carbide, also known as carborundum, is a hard compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive.

[B] Boron

Notes:

Some elements behave chemically both as metals and nonmetals, and are called metalloids. There are total eight of them such as Boron, Silicon, Germanium and Antimony. Most of these elements are used in doping of semiconductors. Elements which are neither metals nor non-metals are called Noble or Inert Gases.

[B] Cesium

Notes:

In 1967, based on Einstein defining the speed of light as the most constant dimension in the universe, the International System of Units isolated two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the meter. Since then, caesium has been widely used in highly accurate atomic clocks. Among alkali metals, cesium melting point 38.4°C has lowest ionization energy Hence, it can show photoelectric effect to the maximum extent.

[A] Allotrope

Notes:

Ozone (O3) is an allotrope of oxygen. Also known as trioxygen, one molecule of ozone is made of 3 oxygen atoms. It is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges.

[A] Electrons in outer most shell

Notes:

Elements in the same group in the periodic table have similar chemical properties. This is because their atoms have the same number of electrons in the outer orbital. Those outer electrons are also called valence electrons. They are the electrons involved in chemical bonds with other elements.

[C] Ash

Notes:

When Magnesium burns in air it reacts with oxygen present in air to form magnesium oxide:

2Mg + O2 —> 2MgO.

Magnesium oxide is a crumbly, whitish powder that looks like ash. The formation of magnesium oxide is a direct combination reaction of two elements magnesium and oxygen.

[C] Gold

Notes:

Ductility is a physical property of a material associated with the ability to be hammered thin or stretched into wire without breaking. Gold, which has a density of 19.32 g/cm3, is the most ductile metal and can be pressed into a thin leaf or drawn out into a long fiber. Silver, Copper and Aluminium are next to gold.