Answer: The correct option is B.
Explanation: There are 2 regions of the solar system.
1) Inner region: There are 4 planets which lie in this region: Mercury, Venus, Earth and Mars. The inner region planets are rocky in nature. The orbit time of these planets around the sun is short. They have 0, 1 or 2 satellites in total. There is no ring system in these planets.
2) Outer region: There are 4 planets which lie in this region: Jupiter, Saturn, Uranus and Neptune. The outer region planets are gaseous in nature. The orbit time of these planets around the sun is long. They have usually more number of satellites around them. Ring system in these planets is very common.
Hence, Mars resides in the inner region of the solar system because it has a rocky surface that one could firmly stand on.
Half-life of a radioactive substance is the time required to reduce the amount of substance to half of its initial amount.
In present case, half-life is material is given as 1000 years and initial amount of material is given as 400 kg
Answer 1) Since, half-life of radio-active substance is 1000 years, therefore after 1st half life, amount of the material will be left to half the initial amount. Hence, amount of substance left after 1000 years = 400/2 = 200 kg.
Answer 2) For 2000 years, radioactive material has crossed 2 times the half life. Therefore , amount of the material will be left to 1/4 the initial amount. Hence, amount of substance left after 2000 years = 400/4 = 100 kg.
Answer 3) For 4000 years, radioactive material has crossed 4 times the half life. Therefore , amount of the material will be left to 1/16 the initial amount. Hence, amount of substance left after 4000 years = 400/16 = 25 kg.
Antimony has two naturally occurring isotopes. Their abundance is given in the pic attached below
"RED" color bends the least when passing through a prism.
Answer : The mole fraction of NaCl in a mixture is, 0.360
Explanation : Given,
Moles of 
= 7.21 mole
Moles of 
= 9.37 mole
Moles of 
= 3.42 mole
Now we have to calculate the mole fraction of .
Now put all the given values in this formula, we get:
Therefore, the mole fraction of NaCl in a mixture is, 0.360
