The enthalpies of all elements in their standard states are
zero
>0
<0
unity
A.
zero
The enthalphy of elements are zero in their standard state.
Volume of CO2 obtained from complete decomposition of 20 g CaCO3 at STP is
2.24 litre
4.48 litre
20 litre
22.4 litre
B.
4.48 litre
CaO +
100 gm of CaCO3, on decomposition, gives 22.4 litre CO2 at STP
20 gm of CaCO3, on decomposition, will give
= = 4.48 litre CO2 at STP.
A golf-ball weigh 40.0 gm. If it is moving with a velocity of 20.0 ms-1, it's de-Broglie wavelength is
1.66 x 10-34 nm
8.28 x 10-32 nm
8.28 x 10-25 nm
1.66 x 10-24 nm
C.
8.28 x 10-25 nm
From de-Broglie equation,
Which of the following, is not a unit of pressure?
Atmosphere
Torr
Pascal
Newton
D.
Newton
Newton is not the unit of pressure. It is the unit of force. Atmosphere, torr and pascal (Pa) are the units of pressure.
1 atm = 1.01 x 105 Pa
1 torr = 133.3 Pa
The shape of an orbital is determined by
n
l
m
s
B.
l
The azimuthal quantum number (l) determines the shape of an orbital. Fore.g.
l = 0 (spherical, s)
l = 1 ( dumb- bell, p) and so on.
Which of the following order of ionisation energy is correct?
B < Be < N < C
Be > B > C > N
B < Be < C < N
Be < B < C < N
C.
B < Be < C < N
Ionisation energy generally increase in a period from left to right. But due to comparatively stabler configuration of Be (1s2, 2s2), it has more ionisation energy than Boron (1s2, 2s2, 2p1) Hence, the correct order is : B < Be < C < N.
Which of the following ions, has smallest size?
Ca2+
Cl-
S2-
K+
A.
Ca2+
Ca2+, Cl-, S2- and K+ are isoelctronic species. In isoelectronic ions, size decrease with increasing nuclear charge. Hence, Ca2+ ion is the smallest among these.
Which is the shortest wavelength line in the Lyman series of the hydrogen spectrum? (R= 1.097 x 10-2 nm-1)
94.21 nm
91.16 nm
911.6 nm
933.6 nm
B.
91.16 nm
For Lyman series,
Hence, for to be smallest, n should be greatest (i.e. )
91.16 nm is the shortest wavelength line in the Lyman series of the hydrogen spectrum.
The significant figures in 1.0024, 1.240 and 0.0020 are respectively
5, 4, 2
3, 3, 1
5, 3, 4
5, 3, 2
A.
5, 4, 2
In 1.0024, all figures are significant.
In 1.240,the significant figures are four (zero tells about precision). Zero before a number are not significant, hence, 0.0020 has only two significant numbers (2 and 0 after 2).
Which of the following acids is monobasic?
H3PO3
H3PO2
H2SO3
H3PO4
B.
H3PO2
H3PO2 or hypophosphorus acid is a monobasic acid. It gives only one type of salt e.g., NaH2PO2.
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