Important PYQs Computer Science Class 12

• A Primary Key is chosen from the set of Candidate Keys in a table.
• Candidate Keys are those that uniquely identify each row and do not contain redundant attributes.
• Out of multiple Candidate Keys, one is selected as the Primary Key, while the rest become Alternate
  Keys.

Other options:
(A) Composite Key: A key made up of multiple columns.
(B) Alternate Key: Candidate keys that are not chosen as the primary key.
(D) Foreign Key: A key that refers to the primary key of another table.

Explanation:
Operator Precedence in Python:
1. Exponentiation (**) has the highest precedence.
2. Division (/) and Floor Division (//) are evaluated next (left to right).
3. Addition (+) comes last.

Step-by-Step Evaluation:
Exponentiation (**): 4**2 = 16
So, the expression simplifies to:
6 + 5 / 16 // 5 + 8

Division (/):5/16 = 0.3125
The expression now becomes:
6 + 0.3125 // 5 + 8

Floor Division (//):0.3125//5=0.0
(Since // gives the floor value of the division result)
Now, we have:
6 + 0.0 + 8

Addition (+):6+0.0+8 = 14.0

Hence the final answer is : 14.0

Explanation:
Understanding strip(): The strip(chars) method removes all occurrences of the characters in chars from both the beginning and the end of the string. It does not remove characters from the middle of the string.

Step-by-Step Execution:
Given String: “text#next”
Characters to Remove: The strip(“t”) function will remove all leading and trailing occurrences of the letter ‘t’ from the string.

Processing:
– The first ‘t’ at the start is removed → “ext#next”
– The last ‘t’ at the end is removed → “ext#nex”

Hence the aswer is : ext#nex

Explanation:The INSERT command in SQL is used to add a new record (row) to a table.

Other options:
(A) UPDATE → Used to modify existing records, not add new ones.
(B) ADD → Not a valid SQL command for inserting records.
(D) ALTER TABLE → Used to modify the structure of a table (e.g., adding/removing columns), not inserting records.

Explanation:
HTML stands for HyperText Markup Language, where:
H → Hyper
T → Text
M → Markup
L → Language
It is the standard language used for creating web pages and web applications.

Other options are related to HTML.

Explanation:
A valid Python identifier follows these rules:
✅ Can contain letters (a-z, A-Z), digits (0-9), and underscores (_).
✅ Cannot start with a digit.
✅ Cannot contain special characters like @, #, $, etc.
✅ Cannot have spaces.
✅ Cannot be a Python keyword.

Other Options:
(A) 2user ❌ Invalid → Cannot start with a digit.
(B) user@2 ❌ Invalid → Contains @, which is not allowed.
(D) user 2 ❌ Invalid → Contains a space, which is not allowed.

Explanation:
– random.randrange(10) generates a random integer from 0 to 9.
– Adding 1 shifts the range to 1 to 10.
– Possible values for Shuffle: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}.
– random.randrange(5) generates a random integer from 0 to 4.
– Multiplying by 10 results in values {0, 10, 20, 30, 40}.
– Possible values for Draw: {0, 10, 20, 30, 40}

(A) Shuffle 1 # Draw 0
Shuffle = 1 ✅ (Valid, since range is 1-10)
Draw = 0 ✅ (Valid, since possible values are {0, 10, 20, 30, 40})
✅ Possible Output

(B) Shuffle 10 # Draw 10
Shuffle = 10 ✅ (Valid, since range is 1-10)
Draw = 10 ✅ (Valid, since 10 is a valid value)
✅ Possible Output

(C) Shuffle 10 # Draw 0
Shuffle = 10 ✅ (Valid, since range is 1-10)
Draw = 0 ✅ (Valid, since 0 is a valid value)
✅ Possible Output

(D) Shuffle 11 # Draw 50
Shuffle = 11 ❌ (Invalid, since Shuffle can only be between 1 and 10)
Draw = 50 ❌ (Invalid, since Draw can only be {0, 10, 20, 30, 40})
❌ Impossible Output

Explanation:
Let’s analyze the given Python code step by step:
a = 10
def convert(b=20):
a = 30 # This is a local variable inside the function
c = a + b
print(a, c) # Prints the local values of ‘a’ and ‘c’

convert(30)
print(a) # Prints the global ‘a’

Step-by-Step Execution:

1. Global variable initialization:
a = 10
– The variable `a` is defined **globally** with the value `10`.

2. Function Definition:
def convert(b=20):
– The function `convert()` is defined with a default parameter `b=20`.

3. Calling `convert(30)`:
convert(30)
– `b` takes the value `30` (because we passed `30` as an argument).
– Inside the function:
a = 30
– A new local variable `a` is created inside the function, which is separate from the global `a`.
c = a + b # c = 30 + 30 = 60
– `c` is calculated as `30 + 30 = 60`.
print(a, c) # Prints: 30 60
– Prints “30 60” inside the function.

4. Printing `a` outside the function:
print(a)
– The global `a` remains unchanged (`a = 10`), because the `a = 30` inside the function was local to `convert()`.
– So, it prints “10”.

Final Output:
30 60
10

Explanation:
In Python, parentheses alone do not make a tuple unless there is a comma inside.
Here, N is simply assigned the value 25, which is an integer.

Other Options:
(B) String → Strings are enclosed in quotes (’25’ or “25”), which is not the case here.
(C) Tuple → A single-element tuple must have a comma, like this: N(25,)
(D) List → Lists are enclosed in square brackets ([]), like: N = [25]

Explanation:
– CHAR is used when the length of the value is fixed, meaning it will always occupy the same number of characters. If the string is shorter than the fixed length, it will be padded with spaces.

– VARCHAR is used for variable-length strings, so it would not be suitable for fixed-length values.
– LONG and NUMBER are not valid MySQL data types for storing alphanumeric strings.

Explanation:
Binary files are stored as a sequence of raw bytes. Unlike text files, which use a specific encoding to represent characters, binary files can store any kind of data, such as images, audio files, video files, compiled software, etc.
Binary files don’t follow a human-readable format, and the bytes are interpreted according to the structure or format the file represents. For example, a .jpg image or a .exe executable file is a binary file.
This is the correct answer because the question asks about files stored in a sequence of bytes without specifying whether it’s for human-readable data (which is typically text).

Other Options:
(A) Text
Text files store human-readable characters, such as letters, numbers, and punctuation. These characters are encoded in a specific format, like ASCII or UTF-8, where each character corresponds to a byte or a series of bytes.
While text files are stored as bytes, they are different from binary files because they follow a more structured, human-readable format. Examples include .txt files or .csv files when they contain text data.

(C) CSV
CSV (Comma-Separated Values) is a type of text file that uses a specific format to store data in rows and columns, often used for spreadsheets or databases.
CSV files are typically text files and are stored as sequences of characters. Even though they can contain alphanumeric data, CSV files still follow a text format and aren’t considered binary files. They are human-readable text, often used in applications like Excel or databases.
While they contain structured data (like numbers and strings), CSV files are still ultimately text files, not binary files.

(D) Notepad
Notepad refers to a text editor, not a file type. When you create a file in Notepad, it saves the content as a text file (usually .txt), which contains human-readable characters stored in a specific encoding.
The content of a Notepad file is still represented in text format (usually as ASCII or UTF-8 encoded characters), so it’s not a binary file.

Explanation:
In Python, the write() method of a file object only accepts strings as arguments.
If you want to write numeric data (integers, floats, etc.) to a text file, you must convert it to a string using str().
Since the reason correctly explains why the assertion is true, option (A) is the best choice.

Explanation:
This results in a SyntaxError, because a non-default (positional) parameter cannot follow a default parameter. In Python, positional parameters must always be written before default parameters in a function header.

Explanation:
The SELECT statement in SQL, when combined with the DISTINCT clause, removes duplicate records from the result set.

Other Options:
(b) DESCRIBE → Used to get the structure of a table, not for filtering duplicates.
(c) UNIQUE → Used in table constraints, not in SELECT queries.
(d) NULL → Represents missing values in SQL, not used for removing duplicates.

Explanation:
Step-by-step calculation:
Multiplication and Division (Left to Right, as they have the same precedence):
16 × 5 = 80
80 ÷ 4 = 20.0
20.0 × 2 = 40.0
40.0 ÷ 5 = 8.0

Subtraction:
8.0 − 8 = 0.0

Explanation:
Loop Iteration 1 (K = 2):

random.randrange(2) generates either 0 or 1 (not 2 because randrange(K) returns values in the range [0, K-1]).
If R = 0, Signal[R] = ‘RED’.
If R = 1, Signal[R] = ‘YELLOW’.

Loop Iteration 2 (K = 1):
random.randrange(1) only returns 0.
So, Signal[R] = ‘RED’.

Possible Outputs:
Since the first value can be either ‘RED’ or ‘YELLOW’, and the second value is always ‘RED’, the only valid output from the options is: YELLOW # RED #

Explanation:
Cardinality in SQL refers to the number of rows in a table.
The COUNT(*) function returns the total number of rows in a table, which represents its cardinality.

Other options:
(a) SUM() → Used to sum values in a numeric column, not to count rows.
(c) AVG() → Calculates the average of numeric values, not row count.
(d) SUM(*) → Invalid function; SUM() requires a numeric column, but * does not refer to a numeric field.

Explanation:
SMTP (Simple Mail Transfer Protocol) is the standard protocol used for sending emails over a computer network. It is responsible for transmitting emails from an email client to an email server and between email servers.

Other Options:
(a) PPP (Point-to-Point Protocol) → Used for establishing a direct connection between two network nodes, not for emails.
(b) HTTP (Hypertext Transfer Protocol) → Used for accessing web pages, not for email transmission.
(c) FTP (File Transfer Protocol) → Used for transferring files between computers, not for sending or receiving emails.

Explanation:
dict is a function to convert a sequence into a dictionary. The dict followed by {} gives a SyntaxError.

Other Options:
(a) d= dict() – Creates an empty dictionary
(b) e = {}
(c) f = []
(d) g = dict{}