What type of reaction takes place when potassium iodide reacts with chlorine gas? a
Double Replacement
b
Decomposition
c
Synthesis
d
Single Replacement

The correct answer is - d. single replacement or displacement.

Explanation:

The displacement or replacement reaction is the reaction in which the less reactive molecule or element is replaced by the more reactive element or molecule in the reaction. If there is only one replacement occurs its termed as a replacement or single replacement reaction.

In this case, if chlorine gas passes through the water solution of KI (potassium iodide), solid iodine and KCl are produced by the displacement or replacement reaction. Here iodine is less reactive so replaced by the more reactive chlorine.

                                 2KI(aq)+Cl2 (g)→2KCl(aq)+I2 (s)

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.