why is there (CN)2 in Sodium Argentocynaide ? provide complete explaination and the chemical bond on the salt

Why is there (CN)2 in the formula of Sodium Argentocynaide

What advantage over an aquatic organisms does a terrestrial organisms have with regard to obtaining oxygen for respiration?

What type of questions asked from the lesson of magnetic effect of electric current 

Wavelength of green light is

A) 400-450 nm

B) 500-550 nm

C) 660-720 nm

D) 720-800 nm