Explanation:
(a) mass number = atomic number + number of neutrons
(the atomic number is the number of protons of an element)
mass number of A = 11 + 12 = 23
mass number of B = 17 + 18 = 35
(b) +1 and -1, respectively
(c) A+ + B- → AB (the first plus sign and the minus sign are superscripts)
In a physical change the appearance or form of the matter changes but the kind of matter in the substance does not. However in a chemical change, the kind of matter changes and at least one new substance with new properties is formed. The distinction between physical and chemical change is not clear cut.
Answer:- D. Double- replacement reaction
Explanations:- In general, the decomposition reactions looks like:
The given reaction looks different than this and so it is not decomposition reaction.
A single-replacement reaction looks like:
Our reaction looks different from this so single-replacement is also not correct.
Synthesis reaction looks exactly opposite to decomposition reaction.
The given reaction is different than this and so it is not synthesis reaction also.
A double-replacement reaction looks like:
In this reaction, the ions are exchanged as could be seen in the general reaction. On reaction side,A is with B and C is with D. On product side, A is with D and C is with B.
The same is happening in the given reaction. Nitrate ion is with lead metal on reactant side and chlorine is with hydrogen, On product side, Chlorine is with lead metal and nitrate ion is with hydrogen. So, ion exchange has taken place here and so this is a double-replacement reaction and choice D is correct.
Answer:
A space station
Explanation:
A space station provides an avenue for scientist to orbit the space and carryout scientific findings. Most space stations are usually controlled under agreement between different countries. The international space station is one such example.
A rover is usually a robotic device that has been pre-programmed and equipped with state of the art devices to carryout explorations on their own.
Most space observations are usually powerful telescopes on the earth surface that monitors events in space.
A satellite is a body that orbits another.
Answer: Option (D) is the correct answer.
Explanation:
Valence shell is the shell present on the outermost core of an atom and electrons present in the valence shell are known as valence electrons.
If an atom has completely filled valence shell then it means the atom is not reactive in nature because it is already stable.
But when an atom has less than eight electrons in its valence shell then it means to attain stability the atom will readily attract electrons towards itself.
As the given element 1 has 8 electrons in its valence shell. Hence, it is not reactive in nature but element 2 has 6 valence electrons. So, in order to attain stability element 2 will readily attract 2 electrons from a donor atom.
Thus, we can conclude that element 2 is more reactive because it does not have a full valence shell, so it will attract electrons.
