tube-light

  1. If the tube-light is fused within six months, we replace it free of cost.
    1a. If the tube-light fuses within six months, we replace it free of cost.
  2. If the tube-light is burnt out within six months, we replace it free of cost.
    2a. If the tube-light burns out within six months, we replace it free of cost.
    Are all correct?

I would not accept any of them.

If the (fluorescent) (light) tube fuses within six months we will replace it free of charge.
If the (fluorescent) (light) tube fuses within six months we will replace it at no cost to yourself/the customer.

Beeesneees,
“If the (fluorescent) (light) tube burns out within six months we will replace it free of charge.”
Is this sentence correct?
“If the (fluorescent) (light) tube is fused within six months we will replace it free of charge.”
“If the (fluorescent) (light) tube is burnt out within six months we will replace it free of charge.”
Are the other two passive forms correct or not?

They are wrong.

fuses
burns out
-no ‘is’

“If the (fluorescent) (light) tube burns out within six months we will replace it free of charge.”
Is it correct?

yes.

You appear to have added the last two sentences to message #1 after I had replied.

Beeesneees,
What is the difference in meaning between “free of cost” and “free of charge”?
Could they not be used interchangeably?

Beeesneees,
What is the difference in meaning between “free of cost” and “free of charge”?
Could they not be used interchangeably?

‘free of cost’ doesn’t make sense.
You could say ‘cost free’ but that is not as fluent and natural.

Beeesneees,

  1. Some hospitals provide treatment free of cost.
  2. Some hospitals provide treatment free of charge.
    Are these sentences correct?

Beeesneees,

  1. Some hospitals provide treatment free of cost.
  2. Some hospitals provide treatment free of charge.
    Are these sentences correct?

Beeesneees,

  1. Some hospitals provide treatment free of cost.
  2. Some hospitals provide treatment free of charge.
    Are these sentences correct?

As I have already clearly indicated ‘free of cost’ does not make sense. Sentence 1 is wrong.