The answer of the question is C. Magnetic fields
The light intensity. The transparency of the filter, the bandwidth of the filter,
Also the color temperature of light source
The main use of litmus is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5–8.3 at 25 °C (77 °F).
