The earth’s core is made of an alloy of
a. iron and nickel.
b. copper and iron.
c. zinc and magnesium.
d. iron and zinc.

Option A

Explanation:

The core of earth has two parts  

a)Outer core – The outer core is made up of molten alloy of iron and nickel. However, it also has traces of dense materials like gold, platinum, and uranium etc. These materials are contained at a very high temperature i.e 9,000 and 13,000 degrees Fahrenheit.  

b)Inner Core – It is composed of solid dense iron but the iron is not in its purest form. It has some impurities such as sulfur etc. It has temperature ranging between 7000 to 9000 degrees Fahrenheit and is responsible for earth's magnetic field.

Hence, option A is correct

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.