Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

In a nuclear reactor

  1. the chain reaction is kept under control by rods of cadmium, which reduces the rate

  2. the thick concrete shield is used to slow down the speed of fast neutrons

  3. heavy water (or graphite) moderate the activity of the reactor
  4. out of $U^{238}$ and $U^{235}$ natural uranium has less that 1% of $U^{235}$
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

Heavy water or Graphite are used as coolants and thick concrete shields are used to prevent radiation.

Multiple choice chemistry nuclear physics nuclear reactor the nuclear power station isotopes and nuclear chemistry

The phenomenon of nuclear fission can be carried out both in a controlled and in an uncontrolled way. Out of the following, the correct statements vis-avis these phenomena are

  1. the fission energy released per reaction is much more than conventional nuclear reactions and one of the products of the reaction is that very particle which initiates the reaction

  2. it is the "surface to volume" ratio of the sample of nuclear fuel used which determines whether or not the reaction would sustain itself as a "chain reaction"

  3. the "control rods" in a nuclear reactor must be made of a material that absorbs neutrons effectively

  4. the energy released per fission as well as energy released per unit mass of the fuel in nuclear fission are both greater than the corresponding quantities for nuclear fusion
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Statements (a), (b) and (c) are correct because of following reasons:

$1)$ If nuclear reactions are to be continued, it is necessary that one of the products works for initiating the reaction further.
For example, in the fission $^{235}U$, $3$ neutrons are released which cause fission of further three $^{235}U$ atoms.
$2)$ There are certain value of surface to volume ratio of the sample of nuclear fuel used which should be satisfied so as the fission can occur.
$3)$ Basically, the fission is continuously carried out due to production of neutrons.
In order to control the reaction, the neutrons should be absorbed.

Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

Metals tend to form:

  1. cations

  2. anions

  3. cations and anions

  4. do not form ions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Metals lose electrons in bonding whilst non-metals gain electrons during ionic bonding hence metals form cations and non-metals form anions. It is difficult for a non metal such as oxygen to lose 6 electrons to form a cation since it would need a lot of energy. When it comes to metals it is also difficult to gain that much elecrons since as electrons are added the effective nuclear charge increases each time.

Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

Metals are usually hard. Hence metals are strong and can withstand heavy loads over them. Due to this property, they are difficult to cut and can be used in the construction of heavy machines, building etc.
On the other hand, non-metals are usually brittle. On hammering them they break into small pieces converting themselves into a fine powder.


In the following elements identify the elements that is relatively brittle?

  1. Sulphur

  2. Diamond

  3. Iron

  4. Magnesium
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Diamond is the hardest non-metallic element which is an exception. Sulphur is a non metal and is relatively brittle while others are metals and are hard, but not brittle.


Therefore, option A is correct.

Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

What are the properties of a metal?

  1. Malleable

  2. Ductile

  3. Form acidic oxides

  4. Conductor
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

Metals are hard and can be casted into thin sheets and wired example Al, iron etc. Therefore they are malleable and ductile respectively.
The valence electrons in metals are delocalized over several atoms that makes them good conductors. Metals react with oxygen to form oxides as:
$Ca+O _2 \rightarrow CaO$
these oxides reacts with water to yield metal hydroxide as:
$CaO+H _2O \rightarrow Ca(OH) _2$
Metal hydroxides are strong bases as they form hydroxide ions and the ion of the particular metal that it is made up of in aqueous phase. Example: When $Ca(OH) _2$ is dissolved in water, it forms two $OH^-$ ions and $Ca^{ 2+ }$ ions. therefore metal oxides are basic.
option A,B, ,D are correct

Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

Which property is not associated with non-metals?

  1. High density

  2. Low melting point

  3. Low tensile strength

  4. Non- ductile
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • As compared to metals, they have low density and will melt at low temperatures. The shape of a nonmetal cannot be changed easily as they tend to be brittle and will break. 
  • Elements that have properties of both metals and nonmetals are called metalloids. They can be shiny or dull and their shape is easily changed.
  • Hence High density is not associated with non-metals and so option A is correct answer.
Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

Which statement is correct for all metals?

  1. Conduct electricity when molten

  2. Gain electrons when they form ions

  3. Have a low density

  4. Have a low melting point
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Solution:- (A) Conduct electricity when molten

Metals conducts electricity in molten state due to delocalised electrions.