Class 8 Science Chapter 11 MCQ

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

Bulb in the set-up A glows more brightly because higher current is flowing through the circuit in set up A, as solution A is better conductor of electricity than that of B.

The liquids that conduct electricity are solutions of acids, bases and salts in water. Vinegar and lemon juice also conduct electricity because they are solution of acids. Similarly, a solution of sodium hydroxide, potassium hydroxide or any other soluble base in water conducts electricity. A solution of copper sulphate, common salt or sodium chloride or any other salt in water also conducts electricity.

Here, all the statements are correct. Hence, your answer will be option [D].

In electroplating factory, the disposal of the used conducting solution is a major concern because it is a polluting waste, therefore it should be disposed-off according to the disposal guidelines of the local authority.

The chemically reactive metals are produced by the chemical effect of electric current. The reactive metals such as sodium, aluminium and magnesium etc., are produced by passing electric current through their compounds in molten state. Sodium metal is produced by the electrolysis of molten sodium chloride whereas aluminium metal is produced by the electrolysis of molten aluminium oxide. In these cases, metal is produced at the negatively charged electrode or cathode because the positively charged ions of metals present in the molten compounds are attracted by the negatively charged or opposite charged electrode. This method is used in the production or extraction of certain metals from their naturally occurring compounds called as “ores”.

Water is a chemical compound and hydrogen and oxygen are elements. When electric current is passed through water. A chemical compound “water” has been decomposed into two elements, hydrogen and oxygen, by the action of electric current. So, this reaction is an example of chemical effect of electric current. The breaking up of water into hydrogen and oxygen is actually a “chemical decomposition reaction” caused by passing an electric current through acidified water which is a conducting liquid. Oxygen gas is formed at the positive electrode which is connected to the positive terminal of the battery and hydrogen gas is formed at the negative electrode which is connected to the negative terminal of the battery.

Here, all the statements are correct. Hence, your answer will be option [D].

The passage of an electric current through a conducting solution causes chemical reactions. As a result, change of colour of solution occurs. This indicates the chemical effect of current.

Here, all the statements are correct. Hence, your answer will be option [D].

Vegetable oil will not conduct electricity because it does not make irons easily.

As we know that electrolytes are of two types; strong electrolytes and weak electrolytes. A strong electrolyte is a liquid which conducts electricity very well but a weak electrolyte is a liquid which conducts electricity to a lesser amount because it contains a lesser number of ions. As example of weak electrolytes are; vinegar or acetic acid solution, lemon juice, carbonic acid solution, ammonium chloride solution, rain water, tap water etc.

Here, all the statements are correct. Hence, your answer will be option [D].

Chromium is used for electroplating to make objects appear shining because chromium has a shiny appearance and it resists scratches.

Here, all the statements are correct. Hence, your answer will be option [D].

In electrolysis process, electrode is one of component is complete the reaction. The chemical reaction takes place between electrodes. Carbon is just like other substance used for electrode but it is widely used in production of silicon and phosphorus. Carbon electrodes have good electrical and thermal conductivity, mechanical strength, chemical purity, easy mounting and accurate machining. It also withstands high temperature, carries large amount of electric current and cost effective. And it is resistant to corrosion also.

Sugar solution in dilute water does not make ions and is a poor conductor of electricity. Therefore, it will not make the current to flow through it and the bulb will not glow.

The decomposition produced by passing current through a conducting liquid is called “Electrolysis”.

We should follow all the three methods, except one which is option [D]. A distilled water salt of the metal to be purified is taken as electrolyte is not required for electrolyte. Hence, your answer should be option [D].

The electroplating of chromium on metal object is called chrome. This procedure is used to reduce corrosion and for decorative purpose. Trivalent chromium plating is done on graphite to avoid oxidation reaction taking place in it. Here, chromium chloride or chromium sulphate is used for electroplating. This is majorly used to make the product thicker. Chromium is plated on steel for decorative purpose and make the metal corrosive resistant. It is used in car parts and utensils. Bakelite and teflon both are special type of plastic.

The silver metal is taken as anode whereas copper metal is taken as cathode. This process is used in electroplating of silver over copper metal. When electricity is passed through electrodes, then silver nitrate ionizes into silver ions and nitrate ions. Copper ions react with nitrate ions to form salt on electrolyte. The silver ions of the electrolytes are deposited on cathode (negative). The silver undergoes reduction reaction and copper undergoes oxidation reaction.

Impure and pure metal are taken as electrode and water-soluble salt of the metal is taken as electrolyte. Here, impure copper metal should take as cathode and pure copper metal taken as anode. Copper sulphate solution is taken as electrolyte. When electricity is passed through electrode, the atoms of the impure metal react with electrolyte and the metal in electrolyte is deposited into cathode. After sometimes, the impure metal electrode becomes thinner and pure metal electrode becomes thicker.

The device which can be used to detect very small current flowing in an electric circuit is light emitting diode or LED.

We should not follow the method is option [C]. For electroplating an iron object with copper metal or copper plating, we should follow the method is: The iron object is made negative electrode. The copper plate is made positive electrode. Copper sulphate solution is taken as electrolyte. Because the metal object on which electroplating is to be done is made the negative electrode or cathode. The metal whose layer is to be deposited is made the positive electrode and a water-soluble salt of the “metal to be deposited” is taken as the electrolyte (the electrolyte contains the metal to be deposited in the form of soluble salt.