CBSE Class 12 Computer Science · MCQ practice
CBSE Class 12 Computer Science Multiple Choice Questions, with Answers
10 practice questions for CBSE Class 12 Computer Science. Every question whose answer is the output of a program was run before publishing, so the answer is what the code really prints — not what it looks like it should.
1. What does the following print?
s = [1, 2, 3] s.append([4, 5]) print(len(s))
- 3
- 4
- 5
- Error
Show the answer
Answer: 4
append() adds the whole list as ONE element, so the length becomes 4. extend() would have made it 5.
append() adds the whole list as ONE element, so the length becomes 4. extend() would have made it 5.
2. What is the output?
t = (1, 2, 3) print(t[-1] + t[0])
- 2
- 3
- 4
- Error
Show the answer
Answer: 4
t[-1] is the last element, 3, and t[0] is 1.
t[-1] is the last element, 3, and t[0] is 1.
3. What does this print?
d = {'a': 1, 'b': 2}
print(d.get('c', 0) + d['a'])- 0
- 1
- 2
- KeyError
Show the answer
Answer: 1
get() returns the default 0 for a missing key instead of raising KeyError.
get() returns the default 0 for a missing key instead of raising KeyError.
4. What is printed?
def f(x, lst=[]):
lst.append(x)
return lst
print(f(1))
print(f(2))- [1] then [2]
- [1] then [1, 2]
- [1, 2] then [1, 2]
- Error
Show the answer
Answer: [1] then [1, 2]
A mutable default argument is created once and reused on every call. This is a classic trap: use None as the default instead.
A mutable default argument is created once and reused on every call. This is a classic trap: use None as the default instead.
5. What does this print?
st = []
for i in range(1, 4):
st.append(i * i)
print(st.pop(), st)- 9 [1, 4]
- 1 [4, 9]
- 9 [1, 4, 9]
- Error
Show the answer
Answer: 9 [1, 4]
pop() removes and returns the top of the stack, which is the last item.
pop() removes and returns the top of the stack, which is the last item.
6. What is the output?
print('Kwickprep'[2:5])- ick
- ickp
- wic
- ckp
Show the answer
Answer: ick
Slicing starts at index 2 and stops before index 5.
Slicing starts at index 2 and stops before index 5.
7. Which SQL clause filters groups rather than rows?
- WHERE
- HAVING
- ORDER BY
- GROUP BY
Show the answer
Answer: HAVING
WHERE filters rows before grouping. HAVING filters the groups afterwards, so it can use aggregate functions.
WHERE filters rows before grouping. HAVING filters the groups afterwards, so it can use aggregate functions.
8. A primary key can be NULL.
- True
- False
Show the answer
Answer: False
A primary key must uniquely identify every row, so it can be neither NULL nor duplicated.
A primary key must uniquely identify every row, so it can be neither NULL nor duplicated.
9. Which file mode erases the existing contents?
- r
- a
- w
- r+
Show the answer
Answer: w
w truncates the file to zero length before writing. a appends instead.
w truncates the file to zero length before writing. a appends instead.
10. In a stack, popping from an empty stack is called
- overflow
- underflow
- traversal
- overwrite
Show the answer
Answer: underflow
Underflow is removing from empty; overflow is adding to a full fixed-size stack.
Underflow is removing from empty; overflow is adding to a full fixed-size stack.
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Get it on WhatsApp Book a free demo classPlease read: these are practice questions written by Kwickprep to help you revise. They are not past examination papers and not a CBSE publication. Questions asked in your school’s viva or examination may differ, and the syllabus can change between sessions — the board’s own document at cbseacademic.nic.in is always the final word. Tell us if you spot a mistake and we will correct it.