The diagram below shows the set-up in which the electrolysis of water takes place.

The test tube containing hydrogen is removed carefully from the apparatus. A lit match stick is brought near the mouth of this test tube. The gas burns with an explosive "pop" sound.

Write a balanced chemical equation for the above electrolysis reaction and indicate whether energy is absorbed or released.

Eight identical, iron blocks are placed on the ground in the two arrangements X and Y as shown below. The block arrangements are kept moist by sprinkling water every few hours.

Which of the arrangements is likely to gather more rust after ten days? justify your answer.

The following chemical equation does not represent a chemical reaction that can take place.
$3 \mathrm{Fe}\left(\mathrm{s}\right)+4{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{Fe}}_3{\mathrm{O}}_4\left(\mathrm{s}\right)$

State what needs to be changed in the equation above for it to represent the correct reaction between $\mathrm{Fe}$ and ${\mathrm{H}}_2\mathrm{O}$.

Trupti mixes an aqueous solution of sodium sulphate$\left({\mathrm{Na}}_2{\mathrm{SO}}_4\right)$ and an aqueous solution of copper chloride $\left({\mathrm{CuCl}}_2\right)$

Will this lead to a double displacement reaction? justify your answer.

Dilip was comparing combination reactions with decomposition reactions.

Which class of chemical substances may be the product of a decomposition reaction but NOT a product of a combination reaction?
 

Tina finds a paper covered with a white substance in a chemistry lab. She keeps the paper near the window of the lab and comes back to pick it up after five hours to take it home. She noticed that the white substance had turned grey.

What could be the most likely substance on the paper that Tina found?

Tina finds a paper covered with a white substance in a chemistry lab. She keeps the paper near the window of the lab and comes back to pick it up after five hours to take it home. She noticed that the white substance had turned grey.

The substance changed from white to grey. Write the chemical equation for this reaction.

Tina finds a paper covered with a white substance in a chemistry lab.She keeps the paper near the window of the lab and comes back to pick it up after five hours to take it home. She noticed that the white substance had turned grey.

State one application of this property of the substance seen in daily life.