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87901.

A radioactive isotope has a half-life of 27 days. Starting with 4g of the isotope, what will be mass remaining after 75 days

Answer»

100g
50g
0.58 g
1.58 g

Solution :`k = (0.693)/(t_(1//2))`
`t = (2.303)/(k) "LOG" (N_(0))/(N)`
`t_(1//2) = 27` days
`k = (0.693)/(27) = 0.0257 "DAY"^(-1)`
`t = (2.303)/(0.0257) "log" (N_(0))/(N)`
`N_(0) = 4g, N =? , t = 75` days
`75 = (2.303)/(0.0257) "log"(4)/(N)`
`N = 0.58g`
87902.

A radioactive isotope having a half life of 2.3 days was received after 9.2 days. It was found that there were 300mg of the isotope in the container. The initial amount of the isotope was

Answer»

1200mg
3600mg
4800 MG
2400mg

Solution :`t_(1//2) = (0.693)/(K) RARR k = (0.693)/(2.3) = 0.3013`
`t= (2.303)/(k) "log" (N_(0))/(N_(t)) rArr "log" (N_(0))/(N_(t)) = (kt)/(2.303)`
`rArr log N_(0) - log N_(t) = (kt)/(2.303)`
`log N_(0) = (0.3013 xx 9.2)/(2.303) + 2.4771 , N_(0) = 4800 mg`.
87903.

A radioactive isotope has a half-life of 20 days. If 100 g of the substance is taken, the weight of the isotope remaining after 40 days is

Answer»

25 g
2.5 g
60 g
40 g

Solution :`N = (40)/(20) = 2`
`:.` Amount LEFT `(N_(0))/(2^(n)) = (100)/(2^(2)) = 25g`
87904.

Aradioactive isotope has t_(1//2) of 10 days. If today 125 g of it is left, what was its weight 40 days earlier ?

Answer»

2g
600g
1g
`1.5g`

Solution :`N=N_(0)((1)/(2))^(n)n=(40)/(10)=4`
`(125)/(1000)=N_(0)((1)/(2))^(4),N_(0)=(125)/(1000)xx2xx2xx2xx2=2g`
87905.

A radioactive isotope has a half-life of 10 days. If today 125 mg is left over, what was its original weight 40 days earlier

Answer»

2g
600 mg
1 g
1.5 g

Solution :`N = N_(0) ((1)/(2))^(n) .n = (40)/(10) = 4`
`(125)/(1000) = N_(0) ((1)/(2))^(4), N_(0) = (125)/(1000) xx 2 xx 2 xx 2 xx 2 = 2g`
87906.

A radioactive isotope decays at such a rate that after 96 minutes only (1)/(8)th of the original amount remains. The half-life of this nuclide in minutes is

Answer»

12
24
32
48

Solution :`lamda = (2.303)/(t) "LOG" ([N_(0)])/([N]) = (2.303)/(96) "log" (1)/(1//8)`
`:. T_(1//2) = (0.693)/(lamda) = (0.693)/(0.0216) = 32.0` MIN
87907.

A radioactive isotope decays at such a rate that after 192 minutes only 1/16 of the original amount remains. The half-life of the radioactive isotope is

Answer»

32 MIN
48 min
12 min
24 min

Solution :`K=(2.303)/(192)log16`
`t_(1//2)-(0.693)/(K)=(0.693)/((2.303)/(192)xx4log2)=48min`
87908.

A radioactive isotope decays as: ._(Z)^(M)A to ._(Z - 2)^(M - 4)B to ._(Z - 1)^(M - 4)C The half lives of A and B are 6 and 10 months respectively. Assuming that initially only A was precent, will it be possible to achieve the radioactive equilibrium for B ? If So, what would be the ratio of A and B at equilibrium? What would happen if the half lives of A and B were 10 and 6 months respectively?

Answer»

Solution :At equilibrium RATIO of amounts of A and B will be
`(N_(A))/(N_(B)) = (t_(1//2)A)/(t_(1//2)B) = (6)/(10) = 0.6`
If the half live of A and B are 10 and 6 MONTS RESPECTIVELY, then B will decay faster than 'A' , hence equilibrium will not be ACHIEVED.
87909.

A radioactive isotope .^(40)K with a half-life of 1.26 xx10^(9) years, decay to .^(40)Ar . A sample of rock from the moon was found to contain both element K and Ar and they are in the rartio 1:7.What is the age of the rock?(Neglect decay of .^(40)K to.^(40)Ca)

Answer»

`2.52 XX 10^(9)` year
`(1.26 xx 10^(9))/("In"2) xx "In" ((7)/(8))` year
`(1.26 xx 10^(9))/("In" 2) xx "In" (7) ` year
`3.78 xx 10^(9)` year

Answer :d
87910.

A radioactive element X decays to give two inert gases in air is:

Answer»

`238_92U`
`226_88RA`
`90^TH`
`89^Ac`

ANSWER :B
87911.

A radioactive element X (atomic weight = 200) shows activity 6.93xx10^(15)dps then find weight of X (in mg). (T_(1//2)=100 "minutes"., N_(A) = 6xx10^(23))

Answer»


ANSWER :20
87912.

A radioactive element with half-life 6.5 hr has 48 xx 10^(19) atoms. Number of atoms left after 26 hr

Answer»

`24 xx 10^(19)`
`12 xx 10^(19)`
`3 xx 10^(19)`
`6 xx 10^(19)`

SOLUTION :`N_(t) = N_(0) ((1)/(2))^(n) = 48xx10^(19) ((1)/(2))^(26//65)`
`= 48 xx 10^(19) ((1)/(2))^(4) = 3xx 10^(19)`
87913.

A radioactive element undergoing decay is left 20% of its initial weight after certain period of time t. How many such periods should elapse from the start for the 50% of the element to be left over?

Answer»

3
4
5
none of these

Answer :D
87914.

A radioactive element resembling iodine in properties is:

Answer»

Astatine
Lead
Radium
Thorium

Answer :A
87915.

A radioactive element resembling iodine in properties is

Answer»

ASTATINE
Lead
Radium
Thorium

Solution :Astatine (At) RESEMBLES in PROPERTIES with IODINE
87916.

A radioactive element is:

Answer»

Sulphur
Polonium
Tellurium
Selenium

Answer :B
87917.

A radioactive element is preset in VIII group of the periodic table. If it emits one alphaparticle, the new position of the nuclide will be

Answer»

VI B
VIII
VIIB
I B

Answer :a,b,C
87918.

A radioactive element has half-life of one day. After three days, the amount of the element left will be

Answer»

1.2 of the original amount
1.4 of the original amount
1.8 of the original amount
1/16 of the original amount

Solution :`n = (3)/(1) = 3, N = (N_(0))/(2^(3)) = (1)/(8)`
87919.

A radioactive element has a half-life period of 140 days . How much of it will remain after 1120 days

Answer»

`(1)/(32)`
`(1)/(250)`
`(1)/(512)`
`(1)/(128)`

Answer :A
87920.

A radioactive element has a half life of one day. After three days, the amount of element left will be:

Answer»

1/2 of the ORIGINAL amount
1/4 of the original amount
1/8 of the original amount
1/16 of the original amount.

Answer :C
87921.

A radioactive element has a half-life of 20 minutes. How much time should elapse before the element is reduced to (1)/(8)th of the original mass

Answer»

40 minutes
60 minutes
80 minutes
160 minutes

Solution :`t_(1//2) = 20` minute, `N = (1)/(9)N_(0)`
USE, `t = (2.303)/(0.693) XX t_(1//2) "log"(N_(0))/(N)`
87922.

A radioactive element has a half life of 20 minutes, How much time should elapse before the element is reduced to 1//8 of its original value

Answer»

A) 160 minutes
B) 60 minutes
C) 30 minutes
D) 40 minutes

Answer :B
87923.

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room

Answer»

1000 days
300 days
10 days
100 days

Solution :Activity `(-(dN)/(dt)) prop N`
`N = N_(0) ((1)/(2))^(n) RARR (N)/(N_(0)) = ((1)/(2))^(n)`
`(1)/(10) = ((1)/(2))^(n) rArr 10 = 2^(n)`
`LOG 10 = n log 2 rArr n = (1)/(0.301) = 3.32`
`t = n XX t_(1//2) = 3.32 xx 30 = 99.6` days
87924.

A radioactive element decays by following three different parallel paths : A overset(lambda_(1))(to) B, lambda_(1) = 5 xx 10^(-2) sec^(-1) 2A overset(lambda_(2))(to) C,lambda_(2) = 3xx10^(-2) sec^(-1) 3A overset(lambda_(3))(to) D, lambda_(3) = 5xx10^(-3) sec^(-1) Calculate average life- time of element (in sec.) [lambda_(1), lambda_(2), lambda_(3) "are decay constans forrespective reactions"]

Answer»


ANSWER :8
87925.

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room ?

Answer»

300 days
10 days
100 days
1000 days.

Solution :LET the PERMISSIBLE activity limit be x, then INITIAL activity would be 10x
`lamda=(0.693)/(30"days")`
`t=(2.303)/(lamda)log"([A]_(0))/([A])`
`=(2.303xx30)/(0.693)"log"(10x)/(x)`
`=99.7"days"~~100` days.
87926.

A radioactive element belongs to the group 14 of the periodic table, it undergoes beta-emission, the product obtained belongs to the following group of the periodic table

Answer»

Group 12
Group 13
Group 15
Group 16

Solution :`._(6)^(14)C overset(beta " decay")RARR ._(7)^(14)N + underset(-1)overset(0)beta`
87927.

A radioactive element decays as X to_(t_(1//2)=30min)^(alpha decay) Y to _(t_(1//2)=2 days)^((-2beta)beta decay)Z. Which of the following statement about this decay process is incorrect?

Answer»

after two hours, less than 10% of the initial X is left
MAXIMUM amount of Y present at any TIME before 30 min is less than 50% of the initial amount of X
atomic number of X and Z are same
the MASS number of Y is greater than X

Answer :D
87928.

A radioactive element (atomic mass = 90 a.m.u.) has half life of 28 years. The number of disintegration per second is :

Answer»

`5.24xx10^(8)`
`5.24xx10^(10)`
`5.24xx10^(-10)`
`5.24xx10^(12)`

Solution :Decay RATE `=lamdaxxN`
`lamda=(0.693)/(t_(1)//2)=(0.693)/(25xx365xx24xx36000)`
`=7.83xx10^(-10)s^(-1)`
No. of atoms in 1 G of element (N)
`=(1)/(90)xx6.023xx10^(23)`
`=6.69xx10^(19)` atoms
Decay rate `=7.83xx10^(-10)xx6.96xx10^(19)`
`=5.24xx10^(10)`
disintegrations per sec.
87929.

(A) Radioactive disintegration process can never go to completion (R ) Radio disintegration process follows first order kinetics

Answer»

Both (A) and (R ) are true and (R ) is the correct explanation of (A)
Both (A) and (R ) are true and (R ) is not the correct explanation of (A)
(A) is true but (R ) is false
Both (A) and (R ) are false

Answer :A
87930.

A radio isotope will not emit

Answer»

GAMMA and alpha rays SIMULTANEOUSLY
gamma rays only
alpha and beta rays simultaneously
beta and gamma rays simultaneously

Solution :In radioactive decay `alpha and beta` particles are not emitted simultaneously, either `alpha or beta` PARTICLE is emitted, one at a TIME.
87931.

A radiator of motor vehicle was filled with 8.2 lt of water to which 2L of methanol (d=0.8 gm//ml) were added, the lowest temp. at which the vehicle can be parked without a danger of getting water in the radiator to freeze is (K_(f) for water =1.86 Km^(-1))

Answer»

`-11.34^(@)C`
`-5.6^(@)C`
`-6.6^(@)C`
`-4.3^(@)C`

ANSWER :A
87932.

A racemic mixture of carboxylic acid having one chiral centre is treated with enantiomerically pure amine. the products formed are :

Answer»

disatereomers (both OPTICALLY active)
diasteremoers (only one is optically active)
RACEMIC mixture
two optically inactive AMMONIUM salts of acid.

Answer :A
87933.

A racemic mixture is a mixture of:

Answer»

MESO and its isomers
d- and its l-isomers in EQUAL proportions
d- and its l-isomers in DIFFERENT proportions
Meso and d-isomers

Answer :B
87934.

A racemic mixture has a net rotation

Answer»

to RIGHT of ORIGINAL PLANE
to LEFT of original plane
to right or left of original plane
zero

Answer :D
87935.

A racemic mixture consistsof

Answer»

equal amounts of enantiomers
DIFFERENT amounts of enantiomers
UNKNOWN amounts of enentiomers
unknown amounts of unknown COMPOUNDS.

Solution :Optical rotation of one enantiomer is EXACTLY balanced by the optical rotation of the other enantiomer TAKEN in exactly equal amounts.
87936.

(A) R-overset(O)overset(||)(C)-Cl fails to give ketone when treated with R-Mg-X, but with R_(2)Cd, ketones is obtained easily. (R) R-Mg-X reacts with acid chloride to form ketone, but R-Mg-X further reacts with ketone readily and form tertiary alcohol.

Answer»

Both (A) and (R) are TRUE and (R) is the correct explanation of (A)
Both (A) and (R) are true and (R) is not the correct explanation of (A)
(A) is true but (R) is false
Both (A) and (R) is false

Answer :A
87937.

Explain elimination reaction. Give example.

Answer»

SOLUTION :ROTATION by an ENANTIOMER CANCELLED by the other.
87938.

A qulalitative analysis of papaverine, an opium alkaloid shown carbon,hydrogen and nitrogen.A quantative analysis gave 70.8% carbon,6.2% hydrogen and 4.1% nitrogen.The empirical formula of papaverrine is :

Answer»

`C_(20)H_(20)N_(2)`
`C_(20)H_(21)O_(4)N`
`C_(10)H_(11)O_(3)N`
`C_(21)H_(20)N`

SOLUTION :N//A
87939.

A quick supply of chlorine gas may be made by reacting crystals of KMnO_4 with a concentrated solution of:

Answer»

POTASSIUM chlorate
Sodium chloride
Bleaching powder
Hydrochloric acid

Answer :D
87940.

A quantity of PCl_(5) ws heated in a 10 litre vessel at 250^(@)C: PCl_(5_(g))hArrPCl_(3(g))+Cl_(3(g)). At equilibrium the vessel contains 0.1 moles of PCl_(5)0.20 mole of PCl_(3)and 0.2 mole of Cl_(2). The equilibrium constant of the reaction is

Answer»

`0.02`
`0.05`
`0.04`
`0.025`

SOLUTION :`K_(c)=([PCl_(3)][Cl_(2)])/([PCl_(5)])=((0.2)/(10)XX(0.2)/(10))/([0.1//10])=0.04.`
87941.

A quantity of PCl_5 was heated in a 10 litre vessel at 250^@ C to show PCL_5(g) hArrPCl_3 + Cl_2 AT equilibrium the vessel contains 0.1 mole of PCl_5 0.20 mole of PCl_3 and 0.20 mole od cl_2 The equilibrium constant of the reaction is :

Answer»

0.02
0.05
0.04
0.025

Answer :C
87942.

A quantity of PCl_(5) was heated in a 10 dm^(3) vessel at 250^(@)C : PCl_(5(g))iffPCl_(3(g))+Cl_(2(g)) At equilibrium, the vessel contains 0.1 mole of PCl_(5) and 0.2 mole of Cl_(2). The equilibrium constant of the reactionis

Answer»

`0.04`
`0.025`
`0.02`
`0.05`

Solution :`{:(,PCl_(5),IFF,PCl_(3),+,Cl_(2)),("MOLES at EQM.","0.1 mole",,"0.2 mole",,"0.2 mole"),("Molar concs.","0.1/10",,"0.2/10",,"0.2/10"):}`
`K=(0.02xx0.02)/(0.01)=0.04`
87943.

A quantity of PCl_(5) was heated in a 10 dm^(3) vessel at 250^(@)C PCl_(5(g)) hArr PCl_(3 (g)) + Cl_(2(g)). At equilibrium the vessel contains 0.1 mole of PCl_(5), 0.2 moles of PCl_(3) and 0.2 moles of Cl_2. The equilibrium constant of the reaction is

Answer»

0.025
0.04
0.05
0.02

Solution :Equilibrium conc. Of `PCl_(5) = (0.1)/(10) = 0.01M`
Equilibrium conc. Of `Cl_(2) = PCl_(3) = (0.2)/(10) = 0.02M`
`RARR K_(C) = ([PCl_(3)][Cl_(2)])/([PCl_(5)]) = (0.02 XX 0.02)/(0.01) = (0.0004)/(0.01)`
`rArr K_(C) = 0.04`
87944.

A quantity of ethyl acetate is mixed with an excess of sodium hydroxide at 25^(@)C. 100 c.c. of the mixture is immediately titrated against 0.05N Hydrochloric acid of which 75 c.c were required for neutralisation. After 30 minutes 50 c.c of the mixture required, similarly 25 c.c of the acid When the original reaction of ester was complete 25 c.c of the mixture required 6.25 c.c of the second order velocity constant ("in mol"//1//"min")(at time =0) of the reaction using concentration in moles per litre and time in minutes. Reactions is first order each w.r.t. NaOH and ester. Indicator chosen for above titrationis such that it gives end point when only hydrochloric acid reacts with NaOH.(log 2= 0.30, log 3= 0.48, In 10 = 2.3)(Given your Answer after multiplying with a factor of 10 and excluding the decimal places)

Answer»


ANSWER :7
87945.

A quantity of electrical charge that brings about the deposition of 4.5 g Al from Al^(3+) at the cathode will also produce the following volume at STP of H_(2)(g) from H^(+) at the cathode:

Answer»

`44.8 L`
`22.4 L`
`11.2 L`
`2.6 L`

ANSWER :D
87946.

A quantity of electrical charge that brings about the deposition of 4.5 g Al from Al^(3+) at the cathod will also produce the following volume (STP) of H_2(g) from H^(+) at the cathode

Answer»

44.8 L
22.4 L
11.2 L
5.6 L

Solution :`AL to Al^(+3)+ 3e^(-) , 27 GM to 3F , 4.5 gm to ? = (4.5 XX 3)/(27)=0.5F`
`2H^(+) + 2e^(-) to H_2 , 2F to 22.4l 0.5 F to ?`
Volume of `H_2 ` from ` H^+` at cathode `= (0.5)/(2) xx 22.4 = 5.6l`
87947.

A quantity of aluminium has a mass of 54g . What is the mass of same number of magnesium atoms?

Answer»

12.1g
24.3g
48.6g
97.2g

Answer :C
87948.

A quantity of 1.92 of methanol was burnt in a constant pressure calorimeter. The temperature of water increased by 4.2^(@)C. If the quantity of water surrounding the inner vessel was 2000 ml and the heat capacity of the inner vessel was 2.02 kJ//^(@)C. Calculate the heat of combustion of methanol. [Specific heat of capacity of H_(2)O = 4.18 J//g^(@) C]

Answer»

SOLUTION :`-726.6 ` kJ/mol
87949.

A quantity of 0.25 M NaOH is added to a solution containing 0.15 mole of aceticacid. The final volume of the solution is 375 mL and the pH of the solution is 4.45. (a) What is the molar concentration of sodium acetate? (b) How many mL of NaOH were added to the original solution? (c) What was the original concentration of the acetic acid?

Answer»

SOLUTION :`(a) 0.048 M (B) 1.9 XX 10^2 ML (C) 0.81 M`
87950.

(A): Pyrolusite is an ore of manganese. (R) : Formula of pyrolusite is Mn_(3)O_(4).

Answer»

Both (A) and (R) are TRUE and (R) is the CORRECT EXPLANATION of (A)
Both (A) and (R) are true and (R) is not the correct explanation of (A)
(A) is true but (R) is FALSE
Both (A) and (R) are false

Solution : (A) is true but (R) is false