(i) Solid $CO_2$ is called dry ice.
(ii) Solid $CO_2$ changes directly into gas at 1 atm pressure.
(iii) Pressure and temperature can change the state of matter.
(iv) Solid $CO_2$ melts into liquid $CO_2$ before becoming gas.
Analyzing Statements About Solid Carbon Dioxide and States of Matter
This solution breaks down each statement provided in the question to determine their accuracy regarding solid carbon dioxide ($CO_2$) and the general principles of matter.
Statement (i): Solid $CO_2$ is called dry ice.
This statement is correct. Solid carbon dioxide is commonly known as "dry ice" because it does not melt into a liquid at atmospheric pressure. Instead, it transitions directly from a solid to a gaseous state, appearing dry.
Statement (ii): Solid $CO_2$ changes directly into gas at 1 atm pressure.
This statement is correct. At standard atmospheric pressure (1 atm), solid $CO_2$ undergoes a process called sublimation. Sublimation is the direct transformation of a substance from the solid to the gas state, bypassing the liquid phase. This is a key characteristic of dry ice under normal conditions.
Statement (iii): Pressure and temperature can change the state of matter.
This statement is correct. Temperature and pressure are the primary factors that determine the state of a substance (solid, liquid, or gas). Increasing temperature typically causes melting or boiling, while increasing pressure can cause condensation or solidification. Conversely, decreasing temperature or pressure can reverse these changes. For example, water freezes into ice at low temperatures and boils into steam at high temperatures, and pressure influences these transition points.
Statement (iv): Solid $CO_2$ melts into liquid $CO_2$ before becoming gas.
This statement is incorrect. As explained in the analysis of statement (ii), solid $CO_2$ sublimes at 1 atm pressure. It transitions directly from solid to gas without forming a liquid phase. Melting into liquid $CO_2$ only occurs at pressures significantly above 1 atm (specifically, above 5.1 atm, the triple point pressure of $CO_2$).
Conclusion
Based on the analysis, statements (i), (ii), and (iii) are correct, while statement (iv) is incorrect under standard atmospheric pressure.
Important Questions from Assertion and Reasons (Notes)
- Given below are two arguments.
(I): A valid deductive argument that also has all true premises is called a sound argument
(II): A strong inductive argument that has all true premises is called a cogent argument
In the light of the above statements, choose the most appropriate answer from the options given below - Given below are two statements one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A A sample survey is usually extensive in scope
Reason R Therfore, both in the number of cases included and in the manner of their selection, it has to be adequately and faithfully representative of a larger population. - Select the option that is true regarding the following two statements labelled Assertion (A) and Reason (R).
Assertion (A): A rubber band is a solid because it regains its original shape when the stretching force is removed.
Reason (R): Solids are rigid and have negligible compressibility. - Two statements are given below. One is Assertion (A) and the other is Reason (R). Choose the correct answer from the options given for these statements.
Assertion (A): Properties of a compound are different from those of its constituent elements.
Reason (R): Compounds are formed by chemical combination of elements in a fixed ratio. - Select the option that is true regarding the following two statements labelled Assertion (A) and Reason (R).
Assertion (A): Copper wire in iron sulphate solution shows no visible reaction.
Reason (R): Copper is less reactive than iron.
