A. phase changing. Physical change is any change in matter that involves the substance going from one physical state to another, and phase change is most commonly used to describe transitions between solid, liquid and gaseous states of matter.
1.A law is an observation; a theory is the explanation of that observation.
2.A theory requires experimentation under various conditions. A law has no such requirements.
3.A theory may become obsolete with time. This is not the case with a law.
4.A theory can be replaced by another better theory; however, this never happens with a law.
5.A theory may be strong or weak according to the amount of evidence available. A law is a universally observable fact.
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Answer:
The unknown element is Carbon.
(a) X is Carbon, its oxide is of acidic nature
(b) C+ O2 → CO2
Explanation:
We are given an unknown element that reacts with oxygen.
X + O2 → XO2
It is given that the oxide XO2 turns blue litmus red which is shown by acids, so XO2 is an acidic oxide. Also X will be a Non metal because Non metallic oxide is Acidic in nature.
The Oxide XO2 is dissolving is water. The oxide upon reacting with water will give an Acid.
XO2 type of oxide is found in the 14th group of the periodic table generally
So we have options like C, Si and Ge as these only have the Acidic oxide.
But when it comes to reactivity with water Only Carbon satisfies the need so the unknown element X is C.
CO2 + H2O → H2CO3 which is an acid.
(a) Element X is Carbon (C), The nature of the compound formed is Acidic.
(b) The reaction given will be as follows
C+ O2 → CO2
Therefore the unknown element is Carbon.
