Cr2O72- + Fe2+ → Cr3+ + Fe3+

14 H⁺ + Cr₂O₇²⁻ + 6 Fe²⁺ ⇒ 2 Cr³⁺ + 7 H₂O + 6 Fe³⁺

Explanation:

The question is missing but I guess it must be about balancing the redox reaction.

We will balance the redox reaction using the ion-electron method.

Step 1: Identify both half-reactions

Reduction: Cr₂O₇²⁻ ⇒ Cr³⁺

Oxidation: Fe²⁺ ⇒ Fe³⁺

Step 2: Perform the mass balance adding H⁺ and H₂O where appropriate (this reaction takes place in acid medium)

14 H⁺ + Cr₂O₇²⁻ ⇒ 2 Cr³⁺ + 7 H₂O

Fe²⁺ ⇒ Fe³⁺

Step 3: Perform the charge balance adding electrons where appropriate

14 H⁺ + Cr₂O₇²⁻ + 6 e⁻ ⇒ 2 Cr³⁺ + 7 H₂O

Fe²⁺ ⇒ Fe³⁺ + 1 e⁻

Step 4: Multiply half-reactions by numbers that make that the electrons gained and lost are equal

1 × [14 H⁺ + Cr₂O₇²⁻ + 6 e⁻ ⇒ 2 Cr³⁺ + 7 H₂O]

6 × [Fe²⁺ ⇒ Fe³⁺ + 1 e⁻]

Step 5: Add both half-reactions and cancel what is repeated

14 H⁺ + Cr₂O₇²⁻ + 6 Fe²⁺ ⇒ 2 Cr³⁺ + 7 H₂O + 6 Fe³⁺

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.