Determine the smallest integer $j$ such that it is possible to fill the fields of the table $10\times 10$ with numbers from $1$ to $100$ so that every $10$ consecutive numbers lie in some of the $j\times j$ squares of the table.

Czech Republic
To determine the smallest integer \( j \) such that it is possible to fill the fields of a \( 10 \times 10 \) table with numbers from \( 1 \) to \( 100 \) so that every \( 10 \) consecutive numbers lie in some \( j \times j \) square of the table, we need to analyze the constraints and construct a valid arrangement.

1. **Understanding the Problem:**
   - We need to place numbers \( 1 \) to \( 100 \) in a \( 10 \times 10 \) grid.
   - Every \( 10 \) consecutive numbers must lie within some \( j \times j \) subgrid.

2. **Initial Consideration:**
   - If \( j = 4 \), then each \( 4 \times 4 \) subgrid can contain at most \( 16 \) numbers.
   - We need to check if it is possible to place \( 10 \) consecutive numbers within any \( 4 \times 4 \) subgrid.

3. **Proof by Contradiction for \( j = 4 \):**
   - Suppose \( j = 4 \) satisfies the condition.
   - Consider the placement of numbers in the \( 10 \times 10 \) grid.
   - If \( j = 4 \), then each \( 4 \times 4 \) subgrid can cover at most \( 16 \) numbers.
   - However, for every \( 10 \) consecutive numbers to lie within a \( 4 \times 4 \) subgrid, there must be an overlap of numbers between adjacent subgrids.
   - This overlap would force some numbers to be repeated or some numbers to be outside the \( 4 \times 4 \) subgrid, which is not possible.

4. **Construction for \( j = 5 \):**
   - We need to show that \( j = 5 \) is sufficient.
   - Consider the following arrangement of numbers in the \( 10 \times 10 \) grid:

\[
\begin{array}{|c|c|c|c|c|c|c|c|c|c|}
\hline
5  & 4  & 3  & 2  & 1  & 100 & 99 & 98 & 97 & 96  \\ \hline
6  & 7  & 8  & 9  & 10 & 91  & 92 & 93 & 94 & 95  \\ \hline
15 & 14 & 13 & 12 & 11 & 90  & 89 & 88 & 87 & 86  \\ \hline
16 & 17 & 18 & 19 & 20 & 81  & 82 & 83 & 84 & 85  \\ \hline
25 & 24 & 23 & 22 & 21 & 80  & 79 & 78 & 77 & 76  \\ \hline
26 & 27 & 29 & 32 & 46 & 55  & 69 & 72 & 74 & 75  \\ \hline
28 & 30 & 33 & 42 & 47 & 54  & 59 & 68 & 71 & 73  \\ \hline
31 & 34 & 39 & 43 & 48 & 53  & 58 & 62 & 67 & 70  \\ \hline
35 & 37 & 40 & 44 & 49 & 52  & 57 & 61 & 64 & 66  \\ \hline
36 & 38 & 41 & 45 & 50 & 51  & 56 & 60 & 63 & 65  \\ \hline
\end{array}
\]

5. **Verification:**
   - Check if every \( 10 \) consecutive numbers lie within some \( 5 \times 5 \) subgrid.
   - For example, numbers \( 1 \) to \( 10 \) lie within the top-left \( 5 \times 5 \) subgrid.
   - Similarly, numbers \( 91 \) to \( 100 \) lie within the top-right \( 5 \times 5 \) subgrid.
   - This pattern continues for all sets of \( 10 \) consecutive numbers.

Thus, the smallest \( j \) that satisfies the condition is \( 5 \).

The final answer is \(\boxed{5}\)