Answer:D
Explanation:according to the law of conservation of energy/momentum, when two bodies collides, their total momentum and energy before and after collision are equal. Given that the two bodies move with the same velocities after collision, means that the law has not been violated since momentum = mass x velocity (where mass is constant) 
 
        
             
        
        
        
Answer:
371.2 mm
Explanation:
The Balmer series of spectral lines is obtained from the formula 
1/λ = R(1/2² -1/n²) where λ = wavelength, R = Rydberg's constant = 1.097 × 10⁷ m⁻¹
when n = 15
1/λ = 1.097 × 10⁷ m⁻¹(1/2² -1/15²)
     = 1.097 × 10⁷ m⁻¹(1/4 -1/225)
     = 1.097 × 10⁷ m⁻¹(0.25 - 0.0044)
     = 1.097 × 10⁷ m⁻¹ 0.245556
     = 2.693 10⁶ m⁻¹
So,
 λ  = 1/2.693 10⁶ m⁻¹
     = 0.3712 10⁻⁶ m
     = 371.2 mm
 
        
             
        
        
        
Choice D, as if it takes up mass then it is matter
        
             
        
        
        
Answer: element 
Explanation:
Couldn't be a compound because contains same type of atoms. Can't be a mixture either because not physically mixed or anything. Isn't a solution ofc because oxygen is a gas.