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
 to  and
 and  = 109677 is the Rydberg Constant. Here
 = 109677 is the Rydberg Constant. Here  and
 and   represents the transitions.
 represents the transitions.
(a)  =2 to
 =2 to  = infinity
 = infinity
              = 109677/4     [since 1/infinity = 0] Therefore,
 = 109677/4     [since 1/infinity = 0] Therefore,  = 4 / 109677 = 0.00003647 m
 = 4 / 109677 = 0.00003647 m
(b)  =4 to
=4 to   = 20
 = 20
             = 6580.62
 = 6580.62
Therefore,   = 1 / 6580.62 = 0.000152 m
 = 1 / 6580.62 = 0.000152 m
(c)   =3 to
=3 to   = 10
 = 10
            = 11089.56
 = 11089.56
Therefore,   = 1 / 11089.56 = 0.00009 m
 = 1 / 11089.56 = 0.00009 m
(d)   =2 to
=2 to   = 1
 = 1
            = - 82257.75
 = - 82257.75
Therefore,   = 1 /82257.75  = - 0.0000121 m
 = 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.
Learn more about the Rydberg's formula athttps://brainly.com/question/14649374
#SPJ4
 
        
             
        
        
        
Answer:
Gamma decay/radiation
Explanation:
Gamma radiation has no mass and no electrical charge which means no change in the atomic number or mass number when gamma rays are emitted.
 
        
             
        
        
        
Answer is 14.5 g L⁻¹.
<em>Explanation;</em>
Here, the question says reduce the units as one. 
The presented units are g/L. To reduce the units to one, what we can do is take L to the upper side. 
This can be done according to the rules of indices;
1 / aˣ = a⁻ˣ
Like that, we can write 1 / L as L⁻¹.
Hence, the reduced unit is g L⁻¹.
But remember to keep a space between when writing two different units.
Actually, this is an unit for density.