General Science GK Questions with Answers – Page 103

The halogens are placed in Group 17 of the modern periodic table. This family has five members - fluorine, chlorine, bromine, iodine and astatine.

An alkene carries one carbon-to-carbon double bond, and that bond uses up two hydrogen atoms that a saturated chain would have held, so the formula drops from CnH2n+2 to CnH2n. Putting n equal to 2 gives C2H4, ethene, the simplest alkene; n equal to 3 gives C3H6, propene.

Alkanes are saturated hydrocarbons in which carbon atoms are joined only by single bonds, and such a chain carries the largest possible number of hydrogen atoms, given by CnH2n+2.

Carbon is a non-metal, so it does not show metallic character; it neither loses electrons to form positive ions nor shows the lustre and malleability of metals.

An ionic compound is a lattice of positive and negative ions held by strong electrostatic attraction, and that force explains all its other properties.

A covalent bond is formed when two atoms share one or more pairs of electrons so that each completes its outermost shell.

A metal loses electrons and a non-metal gains them, so the transfer makes oppositely charged ions that attract each other, and that attraction is an ionic bond.

Sodium is a metal that gives up an electron easily and chlorine is a non-metal that accepts one, so the two form sodium chloride, an ionic compound.

Ionic compounds dissolve well in water but not in kerosene, petrol or other non-polar organic solvents, so this statement is not a property of theirs.

The element with atomic number 56 is barium, and its outermost electron enters the 6s orbital, so it sits in the s-block.

Relative atomic mass is measured against the carbon-12 atom, one-twelfth of whose mass is taken as the standard unit. That unit is the atomic mass unit, written u, and it is defined as exactly one-twelfth of the mass of one atom of carbon-12.

Melting of ice only changes the state of water from solid to liquid; no new substance is formed, so it is a physical change.

Ice melts at 0 degrees Celsius, and 0 degrees Celsius is 273 K on the Kelvin scale. To change Celsius into Kelvin, add 273 to the Celsius reading, so 0 + 273 gives 273 K; the melting point of ice is usually written as 273.15 K in exact work.

The balanced equation is 2FeSO4 → Fe2O3 + SO2 + SO3, so p = 2, q = 1, r = 1 and s = 1.

In a prokaryotic cell the genetic material lies free in the cytoplasm with no nuclear membrane around it, and this poorly defined nuclear region is called the nucleoid.

A medium that holds less water than the cell is a hypertonic medium, so water moves out of the cell by osmosis and the cell shrinks.

Hydrogen is a colourless, odourless and tasteless gas, so none of the colours listed fits it.

Graphite is soft and slippery rather than hard, so this is the statement that is not correct. The difference between the allotropes comes from the way the carbon atoms are joined.

An emulsion is a colloid in which one liquid is spread as fine droplets through another liquid that does not mix with it.

Ethyl acetate is an ester, and esters are the family of organic compounds known for a sweet, fruity smell. It is formed when ethanol reacts with acetic acid in the presence of a little concentrated sulphuric acid, a reaction called esterification, and its formula is CH3COOC2H5.