<h2>Answer:</h2>
A pure metal has specific properties. Sometimes we need that metal but with modified properties. So for the modification of properties we make alloys.
<h3>Explanation;</h3>
- An alloy is a mixture of two elements, one of which is a metal.
- Alloys often have properties that are different to the metals they contain.
- This makes them more useful than the pure metals alone.
- For example, alloys are often harder than the metal they contain.
The decreasing order of wavelengths of the photons emitted or absorbed by the H atom is : b → c → a → d
Rydberg's formula :
,
where λ is the wavelength of the photon emitted or absorbed from an H atom electron transition from 
to 
and 
= 109677 is the Rydberg Constant. Here and represents the transitions.
(a) =2 to = infinity
= 109677/4 [since 1/infinity = 0] Therefore, 
= 4 / 109677 = 0.00003647 m
(b) =4 to = 20
= 6580.62
Therefore, = 1 / 6580.62 = 0.000152 m
(c) =3 to = 10
= 11089.56
Therefore, = 1 / 11089.56 = 0.00009 m
(d) =2 to = 1
= - 82257.75
Therefore, = 1 /82257.75 = - 0.0000121 m
[Even though there is a negative sign, the magnitude is only considered because the sign denotes that energy is emitted.]
So the decreasing order of wavelength of the photon absorbed or emitted is b → c → a → d.
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The balanced thermochemical equation is
KBr ------- K + 1/2 Br2
<h3>What is thermochemical equation? </h3>
A Thermochemical Equation is defined as the balanced stoichiometric chemical equation which includes the enthalpy change, ΔH.
The chemical equation for the decomposition of potassium bromide to its constituent elements bromine ans potassium :
KBr ----- K + Br2
The balanced thermochemical equation of the decomposition of potassium bromide to its constituent elements potassium and bromide as follows
KBr ------- K + 1/2 Br2
As the heat is absorbed in this reaction therefore, heat is positive.
Thus, we concluded that the balanced thermochemical equation is
KBr ------- K + 1/2 Br2
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